Regional Gain Control for Segmented Thin-Film Acoustic Imaging Systems

ABSTRACT

An acoustic imaging system coupled to an acoustic imaging medium to define an imaging surface. The acoustic imaging system includes an array of piezoelectric acoustic transducers formed at least in part from a thin-film piezoelectric material, such as PVDF. The array is coupled to the acoustic imaging medium opposite the imaging surface and formed using a thin-film manufacturing process over an application-specific integrated circuit that, in turn, is configured to leverage the array of piezoelectric actuators to generate an image of an object at least partially wetting to the imaging surface.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a nonprovisional of, and claims the benefit under 35 U.S.C. 119(e) of, U.S. Provisional Patent Application No. 63/169,067, filed Mar. 31, 2021, the contents of which are incorporated herein by reference as if fully disclosed herein.

TECHNICAL FIELD

Embodiments described herein relate to digital imaging systems and, in particular, to acoustic imaging systems configured for use through or with an exterior surface of a portable electronic device.

BACKGROUND

An acoustic imaging system can be used to capture an image of an object at least partially wetting to a surface, often referred to as an “imaging surface.” Certain conventional acoustic imaging systems are implemented with a two-dimensional array of piezoelectric actuators that generate an acoustic pulse directed toward the imaging surface in response to stimulus from control electronics and/or output a voltage signal upon receiving reflections of those acoustic pulses resulting from impedance mismatch boundaries defined by contours of the object wetting to the imaging surface.

In many cases, however, an object may not wet to the imaging surface in a uniform manner, resulting in partially distorted imagery that may not be suitable for biometric authentication or other purposes.

SUMMARY

Embodiments described herein relate to selective gain control for different regions of transducers in thin-film acoustic imaging systems leveraged by electronic devices for biometric imaging. Specifically, a portable electronic device can include an imaging system, as described herein. The imaging system can be coupled to (and/or can partially define) a surface of a housing of the portable electronic device.

This architecture and arrangement defines an imaging area that, if touched by a user, exhibits a pattern of acoustic impedance mismatch that corresponds to that user's fingerprint. More generally, any object that contacts the imaging area causes a pattern of acoustic impedance mismatch that corresponds to surface features of an exterior surface of that object that are in contact with (e.g., wetting to) to the imaging area. In some examples, subsurface acoustic impedance mismatch patterns may also be introduced.

For certain embodiments described herein, a thin-film acoustic imaging system can include an array of imaging tiles, each tile including an array of independently-addressable thin-film acoustic transducers. In some examples, although not required, each transducer or at least one of the transducers is formed from polyvinylidene fluoride (PVDF) disposed over a semiconductor circuit (e.g., in a spin coating operation).

Each of the independently-addressable thin-film acoustic transducers can be conductively coupled to one or more drive control electronics (which can be defined in whole or in part in the semiconductor circuit). The drive control electronics can be configured to apply a high-frequency signal (e.g., 10 MHz-20 MHz) to at least one of the independently-addressable thin-film acoustic transducers to cause that thin-film acoustic transducer to generate an acoustic pulse that propagates through at least a portion of the housing of the portable electronic device toward the imaging area.

Reflections from the imaging area thereafter return to the array of independently-addressable thin-film acoustic transducers which may generate a voltage corresponding to a magnitude of acoustic energy received at least respective transducer. As may be appreciated by a person of skill in the art, the magnitude of acoustic energy received at each transducer may be a function of the acoustic impedance mismatch pattern introduced by an object, such as a finger, engaging/touching the imaging area.

To receive and process these reflections (e.g., in order to reconstruct or otherwise resolve an image of the external surface of the object engaging the imaging area), the imaging system includes a signal processing and/or conditioning pipeline and an analog-to-digital converter.

More specifically, each tile of the array of imaging tiles is associated with a dedicated analog front end responsible for preprocessing and/or conditioning signals received from each thin-film acoustic transducer of that tile. Each dedicated analog front end, of each tile of the array of tiles, is coupled to a shared analog to digital converter. As a result of this architecture, a single high-resolution analog to digital converter (e.g., a successive approximation analog to digital converter) can be used to convert output signals from each independently-addressable thin-film acoustic transducer into a digital value suitable for generating an image of an object in direct or indirect contact with the thin-film acoustic imaging system.

In addition, an acoustic imaging system as described herein can field calibrate by defining and/or leveraging one or more feedback loops to improve imaging contrast and/or uniformity of contrast across the imaging area. For example, an acoustic imaging system as described herein can include a regional gain controller configured to control gain profiles of one or more amplifiers in the signal processing and/or conditioning pipeline and/or gain controllers defined in the digital domain. In this manner and as a result of this construction, the regional gain controller can be configured to boost or attenuate analog or digital signals at one or more different signal processing stages (e.g., before carrier rejection, after carrier rejection, before analog to digital conversion, after analog to digital conversion, and so on), which in turn can lead to improved uniformity of image contrast.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference will now be made to representative embodiments illustrated in the accompanying figures. It should be understood that the following descriptions are not intended to limit this disclosure to one included embodiment. To the contrary, the disclosure provided herein is intended to cover alternatives, modifications, and equivalents as may be included within the spirit and scope of the described embodiments, and as defined by the appended claims.

FIG. 1A depicts an example electronic device incorporating a thin-film acoustic imaging system defining an imaging surface above an active display area of the electronic device, such as described herein.

FIG. 1B depicts an example electronic device incorporating a thin-film acoustic imaging system defining an imaging surface along a housing sidewall of the electronic device, such as described herein.

FIGS. 1C-1F depict an example wearable electronic device incorporating a thin-film acoustic imaging system, such as described herein.

FIG. 2A depicts an example simplified system diagram of a thin-film acoustic imaging system including a rectilinear distribution of piezoelectric transducers, such as described herein.

FIG. 2B depicts an example simplified system diagram of a thin-film acoustic imaging system including a grid distribution of piezoelectric transducers, such as described herein.

FIG. 2C depicts an example simplified system diagram of the thin-film acoustic imaging system of FIG. 1A, taken through section A-A, depicting an acoustic wave propagating toward a user's finger wetting to an imaging surface.

FIG. 2D depicts the simplified system diagram of FIG. 2C, depicting a set of acoustic wave reflections propagating from impedance mismatch boundaries defined by contours of the user's fingerprint.

FIG. 2E depicts an example simplified system diagram of a thin-film acoustic imaging system positioned below, and configured to operate with, a convex imaging surface, such as described herein.

FIG. 2F depicts an example simplified system diagram of a thin-film acoustic imaging system positioned below, and configured to operate with, a concave imaging surface, such as described herein.

FIG. 3 depicts an example simplified system diagram of a thin-film acoustic imaging system, such as described herein.

FIG. 4 depicts an example simplified detail view of a thin-film acoustic imaging system, such as described herein (see, e.g., FIG. 1A, taken through section A-A), including a thin-film piezoelectric actuator.

FIG. 5 depicts a system diagram of a segmented acoustic imaging system including a regional gain controller, as described herein.

FIG. 6 depicts a schematic/signal flow diagram of an analog front end of a tile of a segmented acoustic imaging system including a regional gain controller, as described herein.

FIG. 7 depicts a system diagram of a segmented acoustic imaging system including a regional gain controller, as described herein.

FIG. 8 is a flowchart depicting example operations of a method of operating a thin-film acoustic imaging system including a regional gain controller, such as described herein.

FIG. 9 is a flowchart depicting example operations of another method of operating a thin-film acoustic imaging system including a regional gain controller, such as described herein.

The use of the same or similar reference numerals in different figures indicates similar, related, or identical items.

The use of cross-hatching or shading in the accompanying figures is generally provided to clarify the boundaries between adjacent elements and also to facilitate legibility of the figures. Accordingly, neither the presence nor the absence of cross-hatching or shading conveys or indicates any preference or requirement for particular materials, material properties, element proportions, element dimensions, commonalities of similarly illustrated elements, or any other characteristic, attribute, or property for any element illustrated in the accompanying figures.

Similarly, certain accompanying figures include vectors, rays, traces and/or other visual representations of one or more example paths—which may include reflections, refractions, diffractions, and so on, through one or more mediums—that may be taken by, or may be presented to, represent one or more propagating waves of mechanical energy (herein, “acoustic energy”) originating from one or more acoustic transducers or other mechanical energy sources shown or, in some cases, omitted from, the accompanying figures.

It is understood that these simplified visual representations of acoustic energy are provided merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale or with angular precision or accuracy, and, as such, are not intended to indicate any preference or requirement for an illustrated embodiment to receive, emit, reflect, refract, focus, and/or diffract acoustic energy at any particular illustrated angle, orientation, polarization, color, or direction, to the exclusion of other embodiments described or referenced herein.

Additionally, it should be understood that the proportions and dimensions (either relative or absolute) of the various features and elements (and collections and groupings thereof) and the boundaries, separations, and positional relationships presented therebetween, are provided in the accompanying figures merely to facilitate an understanding of the various embodiments described herein and, accordingly, may not necessarily be presented or illustrated to scale, and are not intended to indicate any preference or requirement for an illustrated embodiment to the exclusion of embodiments described with reference thereto.

DETAILED DESCRIPTION

Embodiments described herein relate to acoustic imaging systems and, in particular, to acoustic imaging systems incorporated into electronic devices leveraged to capture images of fingerprints of users of those electronic devices.

In many implementations, an acoustic imaging system, such as described herein, is positioned behind a display of an electronic device to facilitate through-display imaging of a user's fingerprint when that user touches the display. In other implementations, an acoustic imaging system, such as described herein, can be positioned relative to a housing of a hand-held electronic device to facilitate through-housing imaging of a user's fingerprint when that user handles the hand-held electronic device, such as by grasping a sidewall surface of the housing.

In yet other implementations, an acoustic imaging system, such as described herein, can be positioned relative to a physical input device, such as a button (e.g., a power button) or crown, or key (e.g., of a keyboard), to facilitate imaging of a user's fingerprint when that user interacts with the physical input device. In still other examples, an acoustic imaging system, such as described herein, can be incorporated into any suitable location of any suitable electronic device and leveraged for any suitable imaging purpose, whether biometric or otherwise. These preceding examples are not exhaustive.

For example, an imaging system can be used for input sensing and/or session management. For example, a fingerprint my be recognized as having moved over time (e.g., which may be interpreted as an input) and/or a fingerprint or surface contact image (e.g., from a hand, glove, wrist, and so on) may be recognized as having recently changed by at least a threshold amount, indicating that a user operating the electronic device has changed. In this example, active sessions (e.g., web sessions, authenticated application sessions, elevated user privilege sessions) may be invalidated or otherwise terminated. Many examples and use cases for an imaging system as described herein are possible.

In some examples, a single electronic device can include multiple different acoustic imaging systems configured in different ways and for different purposes. For example, a tablet computing device may include a first acoustic imaging system within a button of the tablet and a second acoustic imaging system behind a display of the tablet. The first acoustic imaging system may be configured for biometric authentication (e.g., fingerprint recognition) whereas the second acoustic imaging system may be configured to detect user input, such as touch input to the display. In these examples, the several acoustic imaging systems may be configured for imaging at different resolutions. For example, the first acoustic imaging system may be configured for higher resolution imaging than the second acoustic imaging system.

For simplicity of description, embodiments described herein reference an acoustic imaging system including a two-dimensional array of piezoelectric actuators that may be coupled to an “acoustic imaging medium.” In many examples, an acoustic imaging medium as described herein, may be a portion of a housing of an electronic device. In other cases, the acoustic imaging medium may be a liquid or gas, such as air.

In some examples, an acoustic imaging medium defined through an electronic device housing can exhibit a generally rectangular cross-sectional profile defined by two substantially parallel opposing surfaces, such as an interior surface of the housing and an exterior surface of the housing. In other cases, an acoustic imaging medium defined through an electronic device housing can exhibit a curved cross-sectional profile defined by a planar surface opposite a curved surface, such as a planar interior surface of the housing and a curved exterior surface of the housing. Many implementations are possible.

In many examples, a two-dimensional array of piezoelectric actuators is adhered, via a thin layer of impedance-matching adhesive (e.g., micrometer scale, for example 1-5 μm) to one acoustic imaging medium surface, thereby defining an opposite surface surface as an “imaging surface” or an “imaging area.” For example, if a thin-film piezoelectric actuator is coupled to an interior surface of an electronic device housing, a portion of the exterior surface of that electronic device housing opposite the thin-film piezoelectric actuator defines the imaging surface. In this example, the material of the housing (e.g., metal, plastic, glass, ceramic, and so on) defines the acoustic imaging medium.

As may be appreciated by a person of skill in the art, a piezoelectric actuator can be manufactured in a number of suitable ways. In some conventional systems, a piezoelectric actuator can be formed in a microelectromechanical machining process that defines a vacuum cavity backing a sheet of piezoelectric material. If a voltage is applied across the piezoelectric material, the material can compress or expand in a direction, thereby generating a pulse of mechanical energy that can propagate through any acoustic imaging medium to which the actuator is coupled.

However, manufacturing a microelectromechanical piezoelectric actuator is a multistage process that is expensive, time consuming, and subject to substantial error. For example, in many cases, forming vacuum cavities suitable for a large array of acoustic transducers requires a process that is incompatible with CMOS processes necessary to define one or more circuits or traces. As a result, different manufacturing steps are required which, in turn, requires at least one alignment step during manufacturing. As may be appreciated by a person of skill in the art, alignment operations during manufacturing increase rejection rates and necessitate high tolerance for error, which informs and impacts overall design.

To account for these and other issues with conventional acoustic imaging systems, embodiments described herein leverage thin-film layers that exhibit piezoelectric properties to define arrays of acoustic transducers. Such layers can be formed over existing integrated circuits, which in turn means that transducer layers can be formed in a single contiguous process with CMOS layers, eliminating any need for repositioning or realignment.

In addition, as a result of the thin-film architecture(s) described herein, a requirement for a backing layer (such as a vacuum cavity, required of conventional microelectromechanical piezoelectric actuators) is eliminated and, thus, acoustic impedance of a two-dimensional array of piezoelectric actuators can be increased relative to conventional microelectromechanical designs. As a result of increased acoustic impedance of the thin-film piezoelectric actuators, an acoustic imaging system such as described herein can be closer to impedance matched to materials with high acoustic impedance, such as glass or metal, substantially more effectively than conventional acoustic imaging designs.

In a more general, non-limiting, phrasing, an acoustic imaging system such as described herein can be used to capture images of objects wetting to imaging surfaces defined by high-impedance materials, exhibiting increased power efficiency and increased signal-to-noise ratio. As a result, an acoustic imaging system such as described herein can be leveraged by, as one example, a portable electronic device to capture an image of a user's fingerprint through glass and/or metal, such as may be used to form a housing of the electronic device.

As a result of these described constructions, one or more of the thin-film piezoelectric actuators can generate an acoustic pulse toward the imaging surface through a body or bulk of the acoustic imaging medium. As the propagating acoustic pulse reaches the imaging surface, which defines an acoustic boundary, a portion of the acoustic pulse may reflect back towards the array and a portion of the acoustic pulse may traverse the acoustic boundary and propagate into another acoustic imaging medium interfacing the imaging surface (e.g., air, an object wetting to the imaging surface, and so on). This boundary is an acoustic impedance mismatch boundary.

The acoustic imaging system, in these and other related examples, can quantify properties of said reflections by sampling voltages output from one or more thin-film piezoelectric transducers of the two-dimensional array.

In particular, output voltage samples over time may correspond to amplitude of the reflections, which, in turn, can be correlated to the acoustic impedance of the object (and, in particular, the acoustic impedance mismatch between the acoustic imaging medium and the object) wetting to the imaging surface. For example, in the case of a user's fingerprint touching the imaging surface, ridges of the user's fingerprint introduce a different acoustic impedance mismatch than the acoustic impedance mismatch introduced by air enclosed by a valley of the user's fingerprint.

As a result of this arrangement, the acoustic imaging system can be leveraged to generate an image of acoustic impedance mismatches defined by contours of an object at least partially wetted to the imaging surface.

For example, the acoustic imaging system may drive individual thin-file piezoelectric transducers to generate acoustic pulses (e.g., by driving the transducers with a wavelet or other voltage signal) and receive reflections resulting therefrom in a sequence or pattern (e.g., row by row, column by column, transducer by transducer, serpentine pattern, and so on).

In other cases, multiple transducers can be driven or stimulated by control electronics according to a specific timing pattern (e.g., beamforming) such that multiple acoustic pulses generated by multiple transducers constructively interfere at a target location of the imaging surface. These preceding examples are not exhaustive; it may be appreciated that a two-dimensional array of piezoelectric transducers such as described herein can be leveraged in a number of suitable ways to generate an image, such as described herein.

Further to the foregoing, a thin-film piezoelectric transducer array, such as described herein, can be formed directly atop, over, or an application-specific integrated circuit (“integrated circuit”) configured to stimulate selected piezoelectric transducers of the array with a voltage to cause each stimulated piezoelectric transducer to expand along an axis parallel to an electric field within that transducer induced by the stimulus voltage.

This operation is referred to herein as “driving” a piezoelectric transducer configured in an “integration mode.” In addition, an application-specific integrated circuit is configured to receive and sample, from selected piezoelectric transducers of the array, an output voltage resulting from compression or expansion of that respective piezoelectric transducer. This operation is referred to herein as “sensing” with a piezoelectric transducer configured in a “sense mode.”

Similarly, it is appreciated that an acoustic imaging medium, such as described herein, may in some embodiments form a part of an electronic device display or housing. In such examples, the imaging surface can be any suitable external surface of an electronic device, such as an external surface above a display or an external surface of a housing sidewall.

As a result of this construction, the application-specific integrated circuit can initiate a drive operation with one or more piezoelectric transducers configured in an integration mode to generate one or more acoustic waves.

In further examples, specific signal processing pipelines are described that can improve signal to noise ratios when operating in a sense mode. In particular, in many embodiments, an array of thin-film piezoelectric actuators can be subdivided and/or segmented into segments also referred to as “tiles.” Each tile can include dedicated readout circuitry, referred to herein as an “analog front end.” Each analog front end of each tile can be configured to perform one or more signal conditioning and/or noise reduction operations such as filtering operations (e.g., bandpass, high-pass, low-pass, or other frequency-domain filtering operations), integration operations, amplification operations, attenuation operations, and so on.

Thereafter, outputs from each of the respective analog front ends can be readout by a shared final stage (or stages) that optionally filters additionally and/or converts analog signals to digital values. As a result of this architecture, a single high-quality analog to digital converter with high resolution can be leveraged to convert analog signals from each individual acoustic transducer of the array of acoustic transducers. Similarly, signal conditioning operations can be performed with higher-quality and higher-fidelity circuits and electronics at the tile level. In these embodiments, benefits associated with including high quality components can be balanced against the cost of providing high quality signal processing and conditioning pipelines for all or substantially all transducers of an array.

In addition, the tiled/segmented architecture described herein can be leveraged for parallel processing; while one tile is performing integration and/or sensing operations, other tiles can be performing the same or different integration and/or sensing operations. In such cases, analog values output from one or more of the tiles can be stored in temporary storage (e.g., capacitors) until the shared final stage is available to convert such values into digital values suitable for digital-domain digital operations such as image construction, contrast correction, template matching, de-noising, de-skewing, and so on.

For example, many embodiments can include a regional gain controller. The regional gain controller can be implemented in whole or part in software or hardware. In some cases, the regional gain controller can be implemented in an application-specific integrated circuit, such as described above.

The regional gain controller can be configured to automatically adjust gain of a signal output from a particular transducer, and/or any transducer within a particular region of the transducer array (whether that region is within a single tile, overlaps multiple tiles, or encompasses an entire tile) by controlling a gain profile of one or more digital domain or analog domain amplification stages based, at least in part, on a location of that transducer relative to the imaging area defined by the transducer array. For example, a gain profile associated with a transducer or region of transducers located along an edge of the transducer array may be different than a gain profile associated with a transducer or region of transducers located within a central portion of the transducer array.

In some embodiments, the regional gain controller can be configured to increase gain by a certain amount, may be configured to set gain to a particular value, may be configured to apply a particular frequency-dependent gain profile, and so on. In some embodiments, a gain profile applied by a regional gain controller can attenuate a voltage signal, whereas in other cases the gain profile can be configured to amplify a voltage signal.

In some cases, a gain profile can be associated with a particular region or contiguous group of transducers. The region may be a fixed region or it may be a region of variable dimensions. In some cases, the region may be a contiguous group of acoustic transducers forming a rectangular or square shape. In other cases, an arbitrarily-shaped region may be associated with a particular gain profile.

In some cases, a region associated with a particular gain profile applied by a regional gain controller as described herein can overlap another region associated with a different gain profile. In such examples, transducers within the overlapping region may be associated with a third gain profile that is the average of the first two gain profiles. In other cases, the third gain profile may be associated with one of the two gain profiles (e.g., a larger gain profile may be selected).

In yet other examples, a gain profile can be selected for a particular region based on a beamforming operation performed at that region. For example, a particular region of acoustic transducers may be used to image a portion of the imaging surface. In this example, a first beamforming operation performed with transducers in this region can trigger application of a first gain profile, whereas a second beamforming operation performed with the same region of transducers can trigger application of a second gain profile.

In addition, a regional gain controller as described herein can be configured to selectively tune gain of one or more amplifiers in a single signal processing/conditioning chain. More specifically, gain of selected individual amplifiers may be individually controlled; in some implementations, only a single amplifier gain profile may be modified, whereas in other implementations multiple different amplifiers can be modified in different and/or interrelated ways.

For example, a pre-amplifier associated with an individual transducer may be a voltage controlled gain amplifier that exhibits gain proportional to a voltage applied to a control input thereof. In such examples, pre-amp gain can be controlled by a regional gain controller. In other cases, other amplifiers in the same signal processing/conditioning chain can be tuned and/or controlled by a regional gain controller.

In yet other examples, gain associated with a particular amplifier may be informed by real-time or historical feedback from other systems. For example, in some embodiments, as noted above, an acoustic imaging system can be used for obtaining an image of a fingerprint of a user touching the imaging surface. In these examples, a digital image recognition algorithm and/or processing pipeline can determine certain regions of a fingerprint image exhibiting contrast that falls below a given threshold and/or an average contrast value associated with other parts of the same image. In this example, an output of the image processing pipeline can identify the region of low contrast as a region to increase gain within; thereafter once a new gain profile is applied to signals(s) received from transducers in that identified region, an imaging operation can be performed.

In yet other examples, gain associated with a particular amplifier and/or a gain profile associated with a particular region or set of transducers of an array of acoustic transducers can be informed by an output of an environmental sensor. For example, a humidity sensor can be leveraged to increase amplification, at one or more stages of amplification, as a function of humidity. In other examples, an output of a temperature sensor can be leveraged by a regional gain controller to determine and/or select a gain and/or gain profile to apply to a particular transducer, a particular region of transducers, or any subset thereof, based on or as a function of temperature.

In yet further examples, a regional gain controller can be configured to apply region specific and/or transcoder specific gain in order to calibrate operation of an acoustic imaging system as described herein. For example, a lookup table can be used to tune gain associated with an output of an individual transducer to account for manufacturing defects and/or field wear of that particular transducer. Similarly, a lookup table can be used to tune gain associated with an output of an individual transducer or region or tile of transducers to account for variations between outputs of that transducer, region, or tile when compared against other tiles or transducers of an imaging system as described herein.

In view of the foregoing, it may be appreciated that a region specific gain controller can be leveraged in a number of suitable ways to increase signal to noise ratio and/or contrast uniformity of an image generated by an acoustic imaging system, such as described herein.

These foregoing and other embodiments are discussed below with reference to FIGS. 1A-9. However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these figures is for explanation only and should not be construed as limiting.

Generally and broadly, FIGS. 1A-1B depict example electronic devices that can incorporate an acoustic imaging system that leverages a regional gain controller, such as described herein. In particular, as noted above, embodiments described herein relate to acoustic imaging systems that resolve an image of an object engaging an imaging surface (also referred to as an input surface or imaging area) of an electronic device by generating acoustic pulses (one or more; in some examples constructively or destructively interfering via beamforming and/or phased array excitation techniques) with piezoelectric acoustic transducers.

In particular, embodiments described herein reference thin-film piezoelectric acoustic transducers. However, it may be appreciate that this is merely one example construction; in other embodiments, other piezoelectric transducers, (e.g., pMUT) can be used. In further examples, different combinations of different types of piezoelectric transducers may be used together. For example, a first set of transducers of a first transducer type may be dedicated to generating ultrasonic/acoustic pulses whereas a second set of transducers of a second transducer type may be dedicated to receiving acoustic pulses to generate images therefrom. The first and second transducers may be optimized for transmitting and receiving acoustic energy, respectively.

For embodiments described herein, acoustic pulses propagate through a portion of the housing of the electronic device (more generally referred to herein as the “acoustic imaging medium”) toward the imaging surface and, thereafter, the acoustic imaging system samples voltage signals produced by the same or different piezoelectric acoustic transducers to quantify amplitude and/or phase of reflections of the acoustic pulses from the imaging surface.

As may be appreciated by a person of skill in the art, amplitudes of reflections from the imaging surface correspond to acoustic impedance mismatch boundaries at the imaging surface; some objects wetting to the imaging surface may absorb more acoustic pulse energy (e.g., objects having an acoustic impedance close to that of the acoustic imaging medium) than other objects wetting to the imaging surface (i.e., objects having an acoustic impedance substantively different from that of the acoustic imaging medium).

By iteratively generating acoustic pulses with any suitable waveform or carrier frequency, and characterizing reflections resulting therefrom, an acoustic imaging system, such as described herein, can be leveraged to generate a two-dimensional image (or in further examples, a three-dimensional image), the contrast of which corresponds to acoustic impedance mismatch boundaries which, in turn, correspond to contours of one or more objects wetting to the imaging surface.

In one particular example, an acoustic imaging system may be used to generate an image of a fingerprint of an fingertip wetting to an imaging surface. Portions of that fingerprint that directly contact the imaging surface (e.g., ridges) may reflect a different quantity of acoustic energy and/or may impart a different phase shift to those reflections than portions of that fingerprint that do not contact to the imaging surface (e.g., valleys).

As such, different acoustic impedance mismatches are associated with ridges and valleys of a user's fingerprint and, by mapping acoustic impedance mismatch at different locations of the imaging surface, a two-dimensional image of the fingerprint can be generated which, in turn, can be computer readable and may be leveraged by the electronic device to perform a particular function, such as authentication or identification of a particular user.

For simplicity of description, many embodiments described herein are configured to operate as (or with) a biometric sensor that obtains and analyzes an image of a user's fingerprint when the user touches a display of an electronic device with one or more fingers. It is appreciated, however, that although many embodiments are described herein with reference to obtaining an image of a user's fingerprint, the various systems and methods described herein can be used to perform other operations, or to obtain non-fingerprint information, such as, but not limited to: obtaining an image of a palm; obtaining an image of an ear or cheek; determining the location of a stylus on an imaging surface of an electronic device; determining a physiological characteristic of a user such as heart rate or blood oxygenation; determining characteristics of a non-imaging surface; determining the force with which a user touches an imaging surface; determining the location at which a user touches an imaging surface; determining a user touch or force input to an imaging surface; and so on.

Accordingly, it may be appreciated that the various systems and methods presented below are merely examples and that other embodiments, systems, methods, techniques, apparatuses, and combinations thereof are contemplated in view of the disclosure provided below.

As used herein, the term “image” and the phrase “resolved image” refers to a collection of pixels, the coordinates of which correspond to local surface characteristics of an acoustic imaging medium (or a portion thereof) that may change as a result of a user's fingertip when the fingertip makes physical contact with the acoustic imaging medium at that location.

The area over which a user's fingertip contacts the acoustic imaging medium can be referred to herein as the “contact area.” Typically, a contact area is a subset of an imaging area, but this is not required; in some cases, the contact area can overlap substantially

In many embodiments, the acoustic imaging medium defines an imaging surface of an electronic device such as, but not limited to: a touch-sensitive surface; a touch-sensitive display; a force-sensitive surface; a force-sensitive display; a cover glass of a display; an exterior surface of a housing or enclosure such as a protective outer layer; a sidewall surface of an electronic device; a button surface of an electronic device; a curved sidewall of an electronic device; a side or endcap surface of a rotary input device; and so on. In these embodiments, the contact area typically takes the shape of at least a portion of a pad of a user's fingertip (e.g., an ellipse).

In many embodiments, each pixel of a resolved image corresponds to an attenuation experienced by a reflection of an acoustic pulse propagating to, and reflecting from, that respective pixel location. The amount of attenuation (e.g., an “attenuation coefficient”) at a particular location corresponds to a value (e.g., darkness, lightness, color, brightness, saturation, hue, and so on) of the associated pixel of the resolved image.

For example, the attenuation coefficient may be a number from 0 to 1.0, and the corresponding pixel may include a brightness value from 0 to 255 units. In this example, the attenuation coefficient and the brightness of the corresponding pixel value may be linearly related, although such a relationship is not necessarily required of all embodiments.

The resolution of the resolved image (and thus the number and/or distribution of pixels forming the same) can be based, at least in part, on the expected or average size of various features of the user's fingerprint. In one example, the resolution of the resolved image is greater than 120 pixels per centimeter (approximately 300 pixels per inch). In further examples, the resolution of the resolved image is greater than or equal to 200 pixels per centimeter (approximately 500 pixels per inch). In still further examples, other resolutions may be suitable. In some cases, the resolution of the resolved image may be non-uniform; certain areas of the resolved image may have a higher resolution than other areas.

As may be appreciated, and as noted above, an attenuation coefficient associated with a particular location of the acoustic imaging medium (e.g., a “local attenuation coefficient”) changes when a fingertip (or more particularly, a “feature” of a fingertip such as a ridge or a valley) is in physical contact with, or otherwise “wets” to, the acoustic imaging medium (e.g., metal, plastic, glass, and so on) at that specific location. This is due to an acoustic impedance mismatch introduced by the wetting of the fingertip (or feature) to the acoustic imaging medium at that location.

As noted above, the term “wetting” and related terminology refers to the spreading and/or partial compression of an object (often a solid object such as a finger), or the outermost surface of the same, when the object physically contacts or touches a surface.

For example, a fingertip wets to the surface of the acoustic imaging medium when the user presses the fingertip against the acoustic imaging medium, causing the ridges of the fingerprint to compress and spread by a certain amount, thereby displacing substantially all air between the ridges of the fingerprint and the surface of the acoustic imaging medium,

For example, as noted above, a feature of a fingertip in direct physical contact with the acoustic imaging medium at a particular location (e.g., a ridge of a fingerprint) attenuates an acoustic pulse propagated toward it, thereby affecting the value of the associated pixel of the resulting image. Conversely, a feature that does not wet to the surface of the acoustic imaging medium (e.g., a valley of a fingerprint) may not substantially attenuate acoustic pulses propagated therethrough, similarly not affecting the value of the associated pixel of the resulting image.

In this manner, the value of each pixel of the resolved image corresponds to whether or not a feature of a fingertip is wetted to the acoustic imaging medium at that pixel location. More specifically, the pixels of the resolved image correspond to whether a ridge or a valley of a user's fingerprint is present at that pixel location. In this manner, the resolved image may serve as a direct proxy for an image of the user's fingerprint.

Furthermore, different features of a fingertip may introduce different acoustic impedance mismatches, thus resulting in different local attenuation coefficients and different pixel values in the resolved image.

For example, denser features of the fingertip (e.g., scar tissue) wetted to the acoustic imaging medium may change local attenuation coefficient(s) differently than less dense features wetted to the surface of the acoustic imaging medium. In other cases, the force with which the user touches the acoustic imaging medium may affect local attenuation coefficients by compressing the fingertip against the acoustic imaging medium. In this manner, the resolved image may exhibit contrast corresponding to the relative density of features of the fingertip wetted to the acoustic imaging medium.

In yet other examples, environment may effect wetting of a fingerprint to the imaging surface. For example, if a user's finger is particularly dry, the finger may exhibit different acoustic characteristics than if the finger is damp or wet. As such, contrast and/or feature definition for ridges and/or valleys may differ based on how moisturized a particular users finger is at a particular time. Material on the user's finger, such as oil or lotion may also impact imaging contrast. In yet other examples, if a user's finger is partially dirty or soiled, imaging contrast may be effected.

As such, many embodiments described herein include a regional gain controller configured to amplify and/or attenuate certain areas of an image by amplifying or attenuating certain transducers or regions of transducers. As a result of such techniques, contrast between features and contrast uniformity across an image can be dramatically improved. In some cases, a regional gain controller can increase or decrease gain of an early-stage amplifier (e.g., prior to carrier rejection, integration, envelope tracking, or other low-pass/baseband operation) to improve image contrast in one or more regions of an output image. In other cases, a regional gain controller can increase or decrease gain of a later-stage amplifier (e.g., prior to analog to digital conversion, but after baseband conversion) to improve image contrast in one or more regions of an output image. In yet other examples, a regional gain controller can be configured to modify an operation of an analog to digital controller so as to improve image contrast in one or more regions of an output image.

More generally, a regional gain controller can be leveraged as described herein to account for region-specific hardware variations and region-specific imaging abnormalities. For example, certain acoustic transducers among an array of acoustic transducers may be manufactured out of specification; performance of these transducers can be corrected by a regional gain controller such as described herein by modifying gain applied to voltage signals generated by those acoustic transducers. In addition, in some cases an image may include areas of low contrast, which may be due to poor wetting to the imaging surface and/or one or more surface characteristics, such as hydration or cleanliness. In these examples, a regional gain controller can be configured to identify regions of low contrast and/or below-image-average contrast, and cause the acoustic imaging system to perform an imaging operation a subsequent time during which the regional gain controller increase gain in the identified regions and/or decreases gain in other regions.

Generally and broadly, it may be appreciated that an acoustic imaging system as described herein can be configured to automatically and/or in response to feedback adjust gain and/or gain profiles or other amplifier operations or characteristics based, at least in part, on a region and/or location of a particular transducer that generated a voltage signal to be amplified by those amplifiers. In some cases, the regional gain controller can be communicably coupled to and/or may include one or more trained machine learning models configured to select gain coefficients for at least one of a set of amplifiers in a signal processing chain, such as described herein.

More generally, an acoustic imaging system such as described herein is configured to resolve an image of a user's fingerprint (and normalize and/or characterize contrast variations across that image and optionally perform subsequent imaging operations with different analog domain or digital domain amplification/gain characteristics) by resolving an image of the acoustic attenuation effects provided by various features of the fingertip that make physical contact with the acoustic imaging medium at various location. Such an image may be referred to herein as an “acoustic attenuation map” of an acoustic imaging medium or contact area.

In some embodiments, an acoustic attenuation map can be modeled as a matrix, a vector, or as a function, the inputs of which are coordinates that correspond to locations on the acoustic imaging medium. It may be appreciated that an acoustic imaging system such as described herein can obtain, resolve, or estimate an acoustic attenuation map of an acoustic imaging medium (or contact area of the acoustic imaging medium) using any suitable or implementation-specific method or combination of methods, several of which are described in detail below.

FIG. 1A depicts an electronic device 100 a incorporating a thin-film acoustic imaging system defining an imaging surface above an active display area of the electronic device, such as described herein.

As depicted, an electronic device 100 a can be implemented as a portable electronic device such as a cellular phone, although such an implementation is not required and other embodiments may be implemented as, without limitation: input devices; laptop computers; desktop computers; industrial processing interfaces; home automation devices; industrial security devices; navigation devices; peripheral input devices; and so on.

As may be appreciated, for simplicity of illustration, the electronic device 100 a is depicted without many elements and functional components that may be leveraged by the electronic device to perform various operations, including operations related to an acoustic imaging system, such as described herein. For example, although not depicted, it may be appreciated that the electronic device 100 a can include one or more processors, one or more memory elements, one or more data stores, one or more input components or sensors, and so on.

As described herein, the term “processor” refers to any software and/or hardware-implemented data processing device or circuit physically and/or structurally configured to instantiate one or more classes or objects that are purpose-configured to perform specific transformations of data including operations represented as code and/or instructions included in a program that can be stored within, and accessed from, a memory. This term is meant to encompass a single processor or processing unit, multiple processors, multiple processing units, analog or digital circuits, or other suitably configured computing element or combination of elements.

In many embodiments, the processor can be operably coupled to a working memory and/or a long term memory. In these examples, a memory of the electronic device 100 a can be configured to store at least one executable asset that, when accessed from the memory by the processor (and/or loaded into the working memory by the processor) can instantiate an instance of software configured to leverage and/or integrate with an acoustic imaging system as described herein. Such instances of software can be configured for any suitable purpose.

The electronic device 100 a also includes a housing 102 and a display 104 defining an active display area 106. The display 104 is disposed below a protective outer layer to protect the display 104 from damage. In this manner, the protective outer layer above the display forms a portion of the housing 102, defining an exterior surface thereof. In many cases, the protective outer layer can be formed from an optically transparent and mechanically rigid material such as glass, sapphire, polycarbonate, and so on.

In many embodiments, the protective outer layer protecting the display 104 can be manufactured, at least in part, from a material exhibiting a high acoustic impedance, such as glass, crystalline materials, or transparent ceramic. In this context, “high” acoustic impedance refers to materials having an acoustic impedance greater than air and/or greater than organic material, such as a user's finger.

In many embodiments, an acoustic imaging system 108 can be disposed within the housing 102 of the electronic device 100 a. As with other embodiments described herein, the acoustic imaging system 108 can include an array of acoustic transducers that are configured to generate acoustic pulses and to receive reflections (e.g., echoes) thereof.

For example, in some embodiments, the acoustic imaging system 108 can be coupled to (e.g., adhered) an internal surface the protective outer layer of the display 104. As a result of this construction, the acoustic imaging system 108 can be leveraged to resolve an image of an object, such as the pad of a fingertip (e.g., fingerprint) of a user 110, in physical contact with the protective outer layer. More particularly, the acoustic imaging system 108 can be configured to determine an acoustic attenuation map of an imaging surface defined as a portion of an exterior surface of the protective outer layer of the display 104.

In some cases, the acoustic imaging system 108 is configured to generate and/or estimate an acoustic attenuation map of only a portion of the protective outer layer of the display 104. This may increase the speed with which the acoustic attenuation map may be generated and/or estimated by reducing the number of calculations and/or operations required. In the illustrated embodiment, the portion of the protective outer layer is identified with a dotted line enclosing a rectangular area. In other examples, other area shapes are possible.

Once an image of fingerprint (or other biometrically-unique surface characteristics such as handprints, ear prints, and so on) of the user 110 is imaged by the acoustic imaging system 108, the obtained image can be compared to a database of known images to determine if the obtained image, and/or features or information derived therefrom (e.g., vector maps, hash values, and so on), matches a known image.

If an affirmative match (e.g., a match exceeding or otherwise satisfying a threshold) is obtained, the electronic device 100 a can perform a function related to the match. In one example, the electronic device 100 a performs a privacy-sensitive authenticated function, such as displaying financial information on the display 104.

In other embodiments, an acoustic imaging system, such as the acoustic imaging system 108 may be disposed relative to other portions of the housing 102 of the electronic device 100 a, so as to defined imaging surfaces elsewhere than shown in FIG. 1A. For example, FIG. 1B depicts an example configuration in which an acoustic imaging system 108 can be positioned relative to a sidewall of the electronic device 100 b, such that a fingerprint image of a user 110 can be captured while the user 110 grasps the phone.

These foregoing embodiments depicted in FIGS. 1A-1B and the various alternatives thereof and variations thereto are presented, generally, for purposes of explanation, and to facilitate an understanding of various configurations and constructions of a system, such as described herein. However, it will be apparent to one skilled in the art that some of the specific details presented herein may not be required in order to practice a particular described embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions of specific embodiments are presented for the limited purposes of illustration and description. These descriptions are not targeted to be exhaustive or to limit the disclosure to the precise forms recited herein. To the contrary, it will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

For example, it may be appreciated that any number of acoustic imaging systems can be included in an electronic device, such as described herein. Such systems can be associated with any internal or external surface of an electronic device; some constructions may position an acoustic imaging system adjacent to a sidewall surface of an electronic device, whereas others may position an acoustic imaging system below or relative to an active display area of a display. It is appreciated that any suitable number of configurations and constructions are possible in view of the description provided herein.

For example, FIGS. 1C-1F depict an example set of embodiments in which an acoustic imaging system, such as described herein, can be incorporated into various portions of a wearable electronic device such as a smart watch secured to a wrist of a user by a band. As noted above, this is merely one example of an electronic device or, more generally, one example of a wearable electronic device, and it may be appreciated that other constructions and architectures are possible in view of the embodiments described herein.

For example, FIG. 2C depicts a wearable electronic device 100 c that includes a housing 112 enclosing and supporting operational and functional components of the wearable electronic device 100 d. The housing 112 can be formed from any suitable material including plastics, metals, ceramics, glass, and so on. The housing 112 can be rigid or flexible and may be monolithic or formed from multiple discrete sections, layers, or portions of material—which may be the same material or differing materials—and may take any suitable shape. The housing 112 can have rounded or flat sidewalls.

The housing 112 can be secured to a limb of a wearer, such as a wrist, by a band 114. The band 114 can be flexible or rigid and can be formed from any suitable material or combination of materials. The band 114 can be formed from, and/or defined by, a single piece of material or multiple interlocking or interwoven pieces of material. The band 114 can be configured to stretch, flex, and/or bend around or contour to a user's wrist in any suitable manner.

The housing 112 can enclose a display that can be used to render a graphical user interface within an active display area 116 configured to emit light through at least a portion of the housing 112. In some examples, a display defining the active display area 116 can be positioned below a cover glass that defines at least a portion of an exterior surface of the housing 112.

As with other embodiments described herein, the wearable electronic device 100 c can incorporate acoustic imaging system that may be configured in the same manner as described above with respect to FIGS. 1A-1B.

In FIG. 1C, the acoustic imaging system is identified as the acoustic imaging system 108. In this illustration, the acoustic imaging system 108 is disposed relative to the active display area 116 such that when a user 110 interacts with content rendered in the graphical user interface shown by the active display area 116 of the display of the wearable electronic device 100 c, the acoustic imaging system 108 can operate to detect and/or image a fingerprint of the user 110.

The depicted configuration is merely one example; the acoustic imaging system 108 can be disposed in any suitable portion of a wearable electronic device such as described herein. For example, FIG. 1D depicts a configuration in which a wearable electronic device 100 d includes the acoustic imaging system 108 across only a portion of the active display area 116 of the wearable electronic device 100 d.

In other cases, an acoustic imaging system 108 can be included in at least a portion of the band 114, such as shown in FIG. 1E. In this embodiment, a user 110 that touches an exterior surface of the band 114 can engage the acoustic imaging system 108 which, in response, can generate an image of the user's fingerprint. In yet other examples, the acoustic imaging system 108 can be configured to image a surface of the wrist of the user 110.

In other words, in some configurations, the acoustic imaging system 108 can be oriented to direct acoustic imaging functionality toward the user's wrist. In some examples of these configurations, the acoustic imaging system 108 can be configured to detect and/or identify one or more skin characteristics of the epidermis of the wearer (e.g., the user 110).

In other examples of these configurations, the acoustic imaging system 108 can be configured to image subdermal layers of the user's wrist, for either biometric imaging purposed or biometric data collection purposes. For example, in some examples, an acoustic imaging system 108 as described herein that is incorporated into a band 114 and/or a housing of a wearable electronic device such as the wearable electronic devices 100 c, 100 d, or 100 e can be configured to generate an acoustic image of an interior of the user's wrist, such as an image of an artery, a vein pattern, a musculature image, a skeletal image, and so on. Such images, and/or combinations thereof, can be leveraged by the wearable electronic device for authentication purposes and/or biometric data collection purposes.

In yet other embodiments the acoustic imaging system 108 can be incorporated into an exterior surface a rotating input device extending from and/or integrated with the housing 112. For example, as shown in FIG. 1F, a crown 118 can incorporate the acoustic imaging system 108 such that as a user 110 moves his or her finger across the crown to provide a rotating input to the wearable electronic device 100 f, the acoustic imaging system 108 can become in contact with a progressively different portion of the user's fingerprint, thereby progressively building a fingerprint image and/or at least a portion thereof.

In yet further examples, the acoustic imaging system 108 can be incorporated into a sidewall surface of the housing 112. For example, the acoustic imaging system can be positioned relative to a lateral sidewall of the housing 112, through which physical input controls may likewise extend. For example, a button and/or a rotary input device can be included.

Each of these controls may be configured to move and/or rotate in response to an application of pressure or friction by a user, such as the user 110. A degree to which either control moves may be received by the wearable electronic device as an input. For example, the wearable electronic device can receive a degree of rotation of the rotary input device as a scrolling input and may receive a press of the button as a selection input. These foregoing examples are not exhaustive; any suitable input device whether physical or virtual can be included in a wearable electronic device as described herein.

In the illustrated examples, the acoustic imaging system is configured to provide acoustic imaging functionality through a sidewall portion of the electronic device that is separate from other physical or virtual controls (e.g., buttons, rotary input devices, and so on) defined through that sidewall; this is merely one example configuration.

These foregoing embodiments depicted in FIGS. 1C-1F and the various alternatives thereof and variations thereto are presented, generally, for purposes of explanation, and to facilitate an understanding of various configurations and constructions of a system, such as described herein. However, it will be apparent to one skilled in the art that some of the specific details presented herein may not be required in order to practice a particular described embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions of specific embodiments are presented for the limited purposes of illustration and description. These descriptions are not targeted to be exhaustive or to limit the disclosure to the precise forms recited herein. To the contrary, it will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

For example, generally and broadly, it may be appreciated that an acoustic imaging system—and in particular an array of acoustic transducers associated therewith—can take any shape (e.g., rectilinear shapes, circular shapes, square shapes, polygonal shapes, and so on) and can be incorporated into any suitable electronic device or surface or input component thereof. Further, it may be appreciated that a single electronic device can include multiple different and/or discrete acoustic imaging systems. For example, in some embodiments, a first imaging system may be disposed within a button or rotary input device and a second acoustic imaging system may be disposed behind (and/or otherwise relative to) a display of the same wearable, portable, or stationary electronic device.

Generally and broadly, FIGS. 2A-3 depict simplified system diagrams of an acoustic imaging system, such as described herein. Independent of whether the acoustic imaging system of these embodiments is constructed using piezoelectric transducers (which may be d31 or d33), it may be appreciated that the piezoelectric transducers can be coupled to and/or otherwise formed on an application-specific integrated circuit, which in turn may be formed in a reel-to-reel or single-stage thin-film transistor manufacturing process.

As a result of this configuration, an acoustic imaging system such as described herein can be manufactured without a requirement for alignment of an array of microelectromechanical piezoelectric transducers with signal traces, solder pads, or other electrical or mechanical coupling(s). As such, an acoustic imaging system, such as described herein, can be manufactured at a more rapid pace and/or can be coupled to an acoustic imaging medium (such as an electronic device housing as shown in FIGS. 1A-1F) to define an imaging surface in a number of suitable ways, several of which are described below.

Further, it may be appreciated that the following (and foregoing) embodiments may be coupled to an acoustic imaging medium with any suitable adhesive or mechanical fastener or fastening methodology (including friction fit, insert molding and the like). In many embodiments, as may be appreciated by a person of skill in the art, an adhesive and/or mechanical fastener used to couple an acoustic imaging system, such as described herein, to a surface of an acoustic imaging medium (e.g., display, housing, sidewall, and so on) can be selected at least in part based on an acoustic impedance of that material (when cured, cooled, or otherwise in a final manufacturing state).

More specifically, in many embodiments adhesives to couple an acoustic imaging system to an acoustic imaging medium may be selected and/or deposited and/or cured so as to provide an acoustic impedance transition from an acoustic imaging system (and, in particular, an array of piezoelectric transducers of an acoustic imaging system) to the acoustic imaging medium.

In this manner, a person of skill in the art will appreciate, that the acoustic imaging system can be more effectively matched to the acoustic imaging medium and, as a result, can more efficiently operate to obtain an image of an object wetting to the imaging surface, such as a fingerprint wetting to an external surface of an electronic device housing.

For example, and as noted above, embodiments described herein relate generally to methods and systems for operating acoustic imaging systems, such as those integrated into the electronic device(s) depicted in FIGS. 1A-1F. Many acoustic imaging systems described herein can be generalized to a simplified architecture including an acoustic imaging medium (e.g., a substrate; typically a monolithic substrate) with two parallel surfaces such as a top surface and a bottom surface.

For convention herein, the bottom surface is understood to be coupled to (e.g., adhered to or otherwise in mechanical communication with) at least a portion of the acoustic imaging system such that the acoustic imaging system is acoustically/mechanically coupled to the acoustic imaging medium via the bottom surface. Similarly, the top surface of an acoustic imaging medium described herein is understood to define an imaging surface; an object engaging the top/imaging surface may cause reflection(s) back to the bottom surface that, in turn, can be used to generate an image leveraging techniques described herein.

An array of acoustic transducers can be arranged in a pattern and positioned near the bottom surface. As described above, to capture an image of an object engaging the top surface, an acoustic imaging system can cause the array, or only a portion thereof, to propagate an acoustic pulse through the bottom surface of the acoustic imaging medium and toward the object.

When the acoustic pulse reaches the top surface of the acoustic imaging medium, a portion of the acoustic pulse may be reflected back towards the array of acoustic transducers. As noted with respect to other embodiments described herein, the reflection(s) can be collected as an acoustic output from the acoustic imaging medium and an image of the top surface of the acoustic imaging medium can be approximated. In many embodiments, these operations of driving at least a portion of the array and receiving voltage signals from the array (corresponding to reflections from the top surface of the acoustic imaging medium, as referred to as the imaging surface), can be performed at least in part by an application-specific integrated circuit which may include a regional gain controller such as described herein.

In many embodiments, an acoustic imaging system can implement the array of acoustic transducers as a number of individual ultrasonic elements formed from piezoelectric material such as lead zircanate titinate, zinc oxide, aluminum nitride, or any other piezoelectric crystal material.

Piezoelectric materials may be selected for the speed with which the materials can react to an electrical stimulus or excitation and/or mechanical stimulus or excitation. In other words, piezoelectric materials can be selected for certain acoustic imaging systems requiring acoustic pulses of particularly high frequency (e.g., megahertz scale, such as 50 MHz).

In these examples, to capture an image of an object engaging the top surface (e.g., fingertip, stylus tip, and so on), the imaging system can cause one or more array of piezoelectric transducers to propagate an acoustic pulse (e.g., such as a plane wave or as a localized pulse having a specified center frequency) generally normal to the bottom surface and toward the object in order to monitor for any acoustic signals reflected therefrom. As noted above, this operation is referred to herein as “driving” the array of piezoelectric transducers. In other cases, driving a piezoelectric transducer/element may not necessarily generate an acoustic pulse normal to the bottom surface.

For example, as may be appreciated, an acoustic pulse may propagate from a single point source along a generally spherical three-dimensional trajectory. In some examples, such as noted above, acoustic energy propagating along a particular angle from a point source (e.g., a single acoustic transducer) may be timed so as to constructively or destructively interfere with an acoustic pulse output from a different acoustic transducer.

Such embodiments leverage beamforming techniques and/or phased array control techniques to increase signal-to-noise ratios and/or image contrast. It is appreciated that these examples are not exhaustive; other driving/timing/control means may be possible in view of the description provided herein. For simplicity of description, many embodiments described herein reference a control schema in which an application-specific integrated circuit tasked with driving a piezoelectric transducer does so one transducer at a time. It is appreciated, however, that this is merely one example; in other cases, multiple transducers can be simultaneously and or phase-control driven and/or driven in a specifically-timed sequence (e.g., for beamforming purposes).

Notwithstanding the foregoing, and as described in reference to other embodiments described herein, when the acoustic pulse reaches the imaging surface of the acoustic imaging medium, a portion of the acoustic pulse may be reflected from the imaging surface and back towards the array of piezoelectric transducers as a result of the acoustic boundary (e.g., acoustic impedance mismatch) between the imaging surface and the portion of object engaging it.

For example, a ridge of a fingerprint may present a different acoustic boundary when touching the acoustic imaging medium (e.g., soft tissue boundary) than a valley of a fingerprint (e.g., air boundary). Accordingly, a ridge of a fingerprint may reflect the acoustic pulse differently than a valley of a fingerprint. In other words, a ridge of a fingerprint produces a different acoustic output than a valley of a fingerprint.

When the acoustic pulse returns to the array of piezoelectric transducers, the elements can be used to capture the reflection as electrical signals or, more precisely, an application-specific integrated circuit conductively coupled to one or more of the piezoelectric transducers receiving the reflections may include an analog to digital converter configured to sample (at a Nyquist-appropriate frequency) voltage output from the one or more of the piezoelectric transducers. As noted above, this operation is referred to herein as “sensing” or “imaging” with the array of piezoelectric transducers. In other cases, voltage sampling may not be required; capacitive storage may be used (as one example) to determine voltage output at a given time.

For example, when an array of piezoelectric transducers receives a portion of the acoustic reflection affected by a ridge of a fingerprint, that array of piezoelectric transducers may produce an electrical signal that is different than the electrical signal produced by an array of piezoelectric transducers receiving a reflection affected by a valley of a fingerprint.

By analyzing the electrical signals, the imaging system can derive an image of the object engaging the imaging surface of the acoustic imaging medium. For example, each electrical signal can correspond to one pixel of the image. In one embodiment, a pixel corresponding to an electrical signal affected by a ridge of a fingerprint may be lighter than a pixel corresponding to an electrical signal affected by a valley of a fingerprint.

As may be appreciated, this may be due to the fact that the acoustic impedance mismatch between air and the acoustic imaging medium is greater than the acoustic impedance mismatch between a fingerprint ridge and the acoustic imaging medium.

FIG. 2A depicts a simplified block diagram of an acoustic imaging systems that can be used with the electronic device 100 of FIG. 1. The acoustic imaging systems 200 can include one or more acoustic transducers 202. The acoustic transducers 202 can contract or expand rapidly in response to an electrical stimulus such as a voltage or current (e.g., electroacoustic transducer). For example, the acoustic transducers 202 can be formed, in certain embodiments, from a piezoelectric material such as lead zircanate titinate, zinc oxide, aluminum nitride, or any other piezoelectric material and may have a piezoelectric response characterized as d31, d32, or d33.

In many embodiments, the acoustic transducers 202 can be configured for both emitting and detecting acoustic signals. In other words, an acoustic transducer 212 can be used to both transmit an acoustic pulse in response to an electrical stimulus/excitation (such as from a voltage wavelet generated by an application-specific integrated circuit, such as described herein) and, in addition, can generate a voltage signal in response to an acoustic output (e.g., acoustic/mechanical energy received as a reflection) from the acoustic imaging medium.

In many examples, the acoustic transducers 202 can be arranged in a pattern. For example, in some embodiments the acoustic transducers 202 can be arranged in an evenly spaced line such as illustrated in FIG. 2A.

In some embodiments, the acoustic transducers 202 can be arranged in a matrix or grid, as shown in FIG. 2B. In some examples, the matrix of the acoustic transducers 202 can be square or otherwise rectangular. In other examples, the matrix of the acoustic transducers 202 can take other shapes, such as a circular pattern (not shown).

Although many embodiments described herein distribute the acoustic transducers 202 in a uniform pattern (e.g., matrix, square, line, circle, and so on), such uniformity is not necessarily required, and in some examples, different regions may enjoy different concentrations/pitches of acoustic transducers.

The acoustic transducers 202 can be coupled to a controller 204, also referred to as an application-specific integrated circuit. The controller 204 can be configured to provide electrical energy (e.g., voltage signals) to each acoustic transducer 212 independently, or to groups of acoustic transducers collectively/simultaneously. For example, the controller 204 can provide a first voltage signal (e.g., chirp, wavelet, and so on) to a first transducer and a second voltage to a second transducer (e.g., phase-shifted chirp, wavelet, and so on). In addition, the controller 204 can control the duration and magnitude of the electrical energy applied to each independent acoustic transducer 212. Further, the controller 204 can be configured to control a center frequency of any voltage signal applied to the transducers; for example, the controller 204 can be configured to control a center frequency of a wavelet to be greater than 40 MHz, such as 50 MHz.

In many examples, the controller 204 can operate in one or more modes, either simultaneously, according to a duty cycle, or in another suitable manner. In certain embodiments, the controller 204 can have an integration mode.

In other embodiments or implementations, the integration mode can be referred to as an integration mode or a drive mode. Accordingly, as used herein, terms and phrases such as “integration mode” and “drive mode”, may be understood to each refer to the same operational mode of an acoustic imaging system.

When in the integration mode, the controller 204 can be configured to provide electrical energy in the form of a voltage signal having high frequency content (e.g., a center frequency above 40 MHz, such as 50 MHz) to one or more of the acoustic transducers 202 and in response, the acoustic transducers 202 can produce an acoustic output, referred to herein as an acoustic pulse. As may be appreciated the acoustic pulse produced by one or more transducers typically exhibits the same frequency content as the voltage signal used to excite the transducers.

In many embodiments, and as noted above, the acoustic imaging system 200 can be disposed within a housing of an electronic device.

In some examples, the acoustic imaging system 200 can be segmented into an array of sub-portions. Each subportion may include a dedicated controller 204, or at least a dedicated portion of the controller 204. For example, in some embodiments, the acoustic transducers 202 can be arranged in a high aspect ratio (e.g., greater than 1) array of 128×42.

In this configuration, the array can be subdivided into a grid of 4×2 tiles, in which each subportion of the grid includes 32×21 individual acoustic transducers. Each of these individual subgroups of acoustic transducers can be controlled and/or operated independent of each of the other individual subgroups of acoustic transducers. In some examples, each individual subgroup (or “tile”) is associated with a respective dedicated controller 204 which can perform both drive and/or sense operation for that individual tile.

In other cases, only a portion of the operations of a controller (e.g., drive operations, sense operations, filtering operations, beamforming operations and so on) can be dedicated to a particular tile. For example, in some cases, each tile may have a shared analog front end for sensing, may share a drive controller for drive operations, and so on.

In view of the foregoing, it may be appreciated that an array of acoustic transducers as described herein can be subdivided into any set of tiles, which may be rectilinear, square, or may follow any pattern (e.g., tessellating pattern s, concentric patterns, linear patterns, rows and columns, and so on). Each subdivision of an array of acoustic transducers as described herein can be controlled independently with independent control electronics, and/or may be controlled in cooperation with one or more other subdivisions or tiles.

For example, FIG. 2C depicts the acoustic imaging system of FIG. 2A positioned below an acoustic imaging medium 206. As noted with respect to FIG. 1, the acoustic imaging medium 206 can be a portion of a display, a portion of an input device (e.g., button, switch, and so on), or a portion of the housing of the electronic device. The acoustic imaging medium 206 can include active components (e.g., circuits, circuit traces, batteries, and so on) or passive components (e.g., glass sheet, metal sheet, and so on) or a combination thereof.

The acoustic imaging medium 206 defines a bottom surface and an imaging surface. The bottom surface is coupled to the acoustic transducers 202 via an adhesive layer 208, which may be optional. The imaging surface of the acoustic imaging medium 206 is opposite the bottom surface and is configured/oriented to receive an object, such as a finger of a user 210. As with other embodiments described herein, the finger of the user 210 may include one or more features that introduce different acoustic impedance mismatches when wetting to the imaging surface of the acoustic imaging medium 206.

The acoustic transducers 202 can be positioned below the acoustic imaging medium 206 so as to be in acoustic communication with the bottom surface, acoustically coupled to the bottom surface via the adhesive layer 208. In this manner, when an acoustic transducer 212 generates an acoustic wave 214 in response to an excitation from the controller 204 (in the interrogation mode), the acoustic wave 214 can propagate into the acoustic imaging medium 206, through the bottom surface, toward the imaging surface and, in turn, toward any feature(s) of the fingerprint of the user 210, such as a valley 216 or a ridge 218.

While the acoustic wave 214 propagates through the acoustic imaging medium 206 toward the imaging surface, the controller 204 can transition partly or entirely into an imaging mode, such as depicted in FIG. 2D. When in the imaging mode, the controller 204 can be configured to receive, sample, and/or analyze an electrical signal from one or more of the acoustic transducers 202 that corresponds to an acoustic output of the acoustic imaging medium 206 resulting from a portion of a reflection (such as reflections 214 a, 214 b, or 214 c) of the acoustic wave 214 (see, e.g., FIG. 2C), such as may originate as a result of wetting of the ridge 218 to the imaging surface and/or as a result of an air gap captured by the valley 216. It may be appreciated that a certain portion of energy of the acoustic wave 214 may be absorbed by the user's finger; this absorbed energy is depicted as the acoustic wave 214 d.

Phrased in another non-limiting manner, in many embodiments, an acoustic reflection from a particular location along the imaging surface may depend upon whether that location is below the ridge 218 or the valley 216. More particularly, the acoustic boundary between the acoustic imaging medium 206 and the ridge 218 (having an acoustic impedance of soft tissue) may cause a measurably smaller amplitude acoustic reflection than the acoustic boundary between the acoustic imaging medium 206 and the valley 216 (having an acoustic impedance of air).

As noted above, the amplitude of a reflection from a ridge/acoustic imaging medium acoustic boundary may be a smaller than the amplitude of a reflection from a valley/acoustic imaging medium acoustic boundary. In other words, the amplitude of an acoustic reflection 216 c from an area of the imaging surface that is below a ridge 218 may be less than the amplitude of an acoustic reflection 214 a, 214 b from an area of the imaging surface that is below a valley 216. Accordingly, the controller 204, when in an imaging mode, can monitor the amplitude (and/or timing, phase, or any other suitable property) of an acoustic reflection to derive, determine, assemble, or create, an image of the ridges and valleys of a user's fingerprint or, more generally, any suitable contour of any suitable object wetting to the imaging surface.

Accordingly, more generally and broadly, it may be appreciated that an acoustic imaging system such as described herein includes two primary components: an array of acoustic transducers and an application-specific integrated circuit configured to operate in a drive mode and a sense mode. In some examples, the drive mode and the sense mode can be time multiplexed, whereas in other examples, a drive mode may be configured to operate in one region while a sense mode is configured to operate in another region.

A person of skill in the art may readily appreciate that any suitable control schema can be used. For example, in some cases as described herein beamforming techniques can be used to concentrate acoustic energy output from two or more acoustic transducers of an array of acoustic transducers at a particular location. In some examples, beamforming may also be used in a receive mode to spatially filter a received signal or set of received signals.

Further, it may be appreciated that a planar imaging surface is not a requirement of the embodiments described herein. A person of skill in the art may readily appreciated that the systems methods and architectures described herein can be readily applied to image wetting of an object to a non-planar surface. For example, FIG. 2E depicts an acoustic imaging systems 200 can include one or more acoustic transducers 202 communicably coupled to a controller 204 that can be configured to operate in a drive mode and/or a sense mode, such as described above.

The controller, as with other embodiments described herein can operate the one or more acoustic transducers 202 as a monolithic entity (e.g., driving all or substantially all transducers at the same time to generate a plane wave) or may subdivide control of the array of transducers such that only some of the one or more acoustic transducers 202 are actively imaging (e.g., being driven and/or used for sensing) at any given time.

In such examples, it may be appreciated that the controller can execute any suitable sweep pattern, beamforming technique, or spatial or temporal filtering technique. In this example, however, the acoustic imaging medium 206 may take a nonplanar shape, such as a convex shape.

An example implementation in which the acoustic imaging medium 206 has a convex shape may be an implementation in which the acoustic imaging system 200 is incorporated into a sidewall of a housing of an electronic device, such as shown in FIG. 1B. In other cases, the acoustic imaging system 200 can be incorporated into an electronic device that has a curved portion of a housing, such as a smartwatch with a curved exterior surface (which may be a sidewall surface, a crown surface, a button surface, or any suitable exterior surface).

Further to the foregoing, it may be appreciated that convex and planar sensing plat shapes are not limiting; more generally, any acoustic imaging medium geometry and/or acoustic imaging medium side cross-section can be used. For example, FIG. 2F depicts a convex acoustic imaging medium 206 that may be used in certain implementations.

It may be appreciated by a person of skill in the art that an acoustic imaging system as described herein can be incorporated into any suitable electronic device, whether portable or stationary, and may be positioned relative to any suitable acoustic imaging medium or sensing surface or imaging surface. In some examples, the acoustic imaging medium may be planar and formed from glass. In other cases, the acoustic imaging medium may be nonplanar and may be formed from metal, such as titanium.

In yet other examples, the acoustic imaging medium may be curved and/or patterned and the acoustic imaging medium may be a ceramic material. It may be further appreciated that control of an acoustic imaging system may vary by implementation in part due to differences in acoustic propagation speed through different materials. In other words, it may be appreciated that an acoustic imaging system as described herein can be incorporated in to many electronic devices, formed from many different materials, and may necessarily operate and/or be configured to operate in different manners based on the selected implementation.

FIG. 3 depicts a simplified block diagram of an acoustic imaging system 300 having both drive and sense modes of operation. An acoustic transducer array 302 can include two or more acoustic transducers. For example, in some embodiments the acoustic transducer array 302 can include an N×M array of individual transducers, which in turn can be subdivided and/or tiled into an A×B array of tiles, each tile including (N/A)×(M/B) individual acoustic elements. For example, an acoustic array can include 1000×100 acoustic elements, divided into 10×2 tiles. In this example, each tile includes 100×50 transducers. In this example, the array is rectilinear and has a high aspect ratio (e.g., greater than 2.0), but this structure may not be required of all embodiments.

Returning to FIG. 3, conductively coupled to the acoustic transducer array 302 can be a drive controller 304, which may be a portion of an application-specific integrated circuit, such as described herein. The driver controller 304 can be configured to deliver a voltage signal, such as a wavelet with a specified center frequency, to one or more transducers of the acoustic transducer array 302.

In some cases, the drive controller 304 can be implemented as a plurality of drive controllers 304. For example, in such an embodiment, each individual transducer of the array of acoustic transducers 302 can be coupled to a respective one drive controller 304. In another example, a single drive controller 304 can be coupled to a subset or subarray of acoustic transducers of the array of acoustic transducers 302. In these and related embodiments, adjacent transducers (and/or all transducers of the acoustic transducer array 302) can share one or more electrodes or traces associated with the drive controller 304.

Conductively coupled to the acoustic transducer array 302 can be a sense controller 306, which may be a portion of an application-specific integrated circuit, such as described herein. The sense controller 306 can be configured to receive a voltage signal from one or more transducers of the acoustic transducer array 302. As with the drive controller 304, in some cases, the sense controller 306 can be implemented as a plurality of sense controllers 306.

For example, in such an embodiment, each individual transducer of the array of acoustic transducers 302 can be coupled to a respective one sense controller 306. In another example, a single sense controller 306 can be coupled to a subset or subarray of acoustic transducers of the array of acoustic transducers 302. In these and related embodiments, adjacent transducers (and/or all transducers of the acoustic transducer array 302) can share one or more electrodes or traces associated with the sense controller 306.

These foregoing embodiments depicted in FIGS. 2A-3 and the various alternatives thereof and variations thereto are presented, generally, for purposes of explanation, and to facilitate an understanding of various configurations and constructions of a system, such as described herein. However, it will be apparent to one skilled in the art that some of the specific details presented herein may not be required in order to practice a particular described embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions of specific embodiments are presented for the limited purposes of illustration and description. These descriptions are not targeted to be exhaustive or to limit the disclosure to the precise forms recited herein. To the contrary, it will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

For example, acoustic transducers such as described herein can be constructed in a number of ways. In typical embodiments, an acoustic transducer or, more precisely, an array of acoustic transducers, is manufactured using thin-film deposition techniques such that the array is formed over and/or formed with an application-specific integrated circuit that performs drive and sense operations, such as described herein. However, this is merely one example construction; other embodiments in which a stack of layers defining an acoustic transducer is disposed over an application-specific integrated circuit are also possible in view of the description provided herein.

For example, generally and broadly, FIGS. 4-5 depict simplified system diagrams of an acoustic imaging system, such as described herein, that can be formed entirely using a thin-film manufacturing process in which an integrated circuit or any other suitable CMOS or other semiconductor circuitry is formed in substantially the same process as an array of thin-film, individually addressable piezoelectric transducers suitable to generate an acoustic pulse or a phased-array of acoustic pulses, such as described herein.

As a result of these described and related configurations, an acoustic imaging system such as described herein can be manufactured without a requirement for alignment of an array of microelectromechanical piezoelectric transducers with signal traces, solder pads, or other electrical or mechanical coupling(s), as noted above. As such, an acoustic imaging system, such as described herein, can be manufactured at a more rapid and cost-effective pace and/or can be coupled to an acoustic imaging medium (such as an electronic device housing as shown in FIGS. 1A-1C) to define an imaging surface in a number of suitable ways, several of which are described below.

FIG. 4 depicts a simplified detail view of a thin-film acoustic imaging system, such as described herein (see, e.g., FIG. 1A, taken through section A-A), including a piezoelectric actuator formed from a thin film that exhibits a piezoelectric property or response, such as polyvinylidene fluoride (PVDF) or trifluoroethylene (TrFE). In some cases, the thin film may be formed from a copolymer such as a vinylidene fluoride and trifluoroethylene blend (e.g., PVDF-TrFE). In some cases, a material such as PVDF-TrFE may be selected due at least in part to simplicity of manufacturing and CMOS-compliant annealing temperatures.

In this embodiment, a high impedance stack of layers 400 is shown. The high impedance stack of layers 400 defines a piezoelectric element that is also referred to as an acoustic transducer. The transducer is configured to convert acoustic energy into electrical potential and vice versa.

In this example, the high impedance stack of layer 400 includes a thin-film piezoelectric layer 402 that is configured to expand and contract along a vertical axis. The thin-film piezoelectric layer 402 may be monolithic or may be segmented and/or divided to define multiple discrete acoustic transducers. For simplicity of illustration, only a single acoustic transducer is shown in FIG. 4, but it may be appreciated that the thin-film piezoelectric layer 402 may be used to define multiple discrete acoustic transducer elements.

The thin-film piezoelectric layer 402 is supported by a support layer 404 (which may also be referred to as an oxide layer, or any other non-conductive insulating layer of material; the layer may be contiguous and/or monolithic or may be formed from multiple layers of material) that encloses a first electrode 406 (which is understood as a portion of a first electrode layer, in array-based acoustic imaging system embodiments; in such examples, the first electrode 406 is a member of an array of electrodes, each of which is isolated from each other and/or conductively decoupled from one another to define an array of electrically distinct and individually-addressable electrodes) against a bottom surface of the thin-film piezoelectric layer 402.

The support layer 404 can be made of a metalloid oxide, such as silicon dioxide. In such embodiments, the support layer 404 may be referred to as a metalloid oxide layer, a passivation layer, an encapsulation layer, or a dielectric layer.

The first electrode 406 can be made from a metallic, and electrically conductive, material such as aluminum. A second electrode 408 (which, as with the first electrode layer is understood as a portion of a second electrode layer, in array-based acoustic imaging system embodiments; the layer may be monolithic or segmented, as described above with respect to the first electrode layer) is disposed onto a top surface of the thin-film piezoelectric layer 402, and may also be made from a metal material, such as molybdenum. In other cases, other metal materials or electrically conductive materials may be used.

The second electrode 408 may be coupled, via an optional adhesive/epoxy layer 410, to a lower surface of an acoustic imaging medium 412. In other cases, the optional adhesive/epoxy layer 410 may be, or may include, a passivation material, such as SiO2.

As a result of this construction, a controller 414 (which may be a portion of an application-specific integrated circuit, such as described herein) can be conductively coupled to the first electrode 406 and the second electrode 408 via one or more routing traces (such as the traces 416, 418) so that the controller 414 can both drive the thin-film piezoelectric layer 402 and sense electrical signals from the thin-film piezoelectric layer 402.

More specifically, as a result of the depicted construction, a voltage signal (such as a chirp signal or a wavelet) output from the controller 414 can cause a voltage potential difference between the first electrode 406 and the second electrode 408 (polarity and/or frequency content of the voltage may vary from embodiment to embodiment) thereby causing the thin-film piezoelectric layer 402 to vertically expand or contract in proportion to the voltage signal which, in turn, results in a mechanical deformation of the thin-film piezoelectric layer 402 along a direction perpendicular to a lateral axis, normal to the lower surface of the acoustic imaging medium 412, thereby generating an acoustic pulse through the adhesive/epoxy layer 410 that can, thereafter, propagate into and through the acoustic imaging medium 412.

Thereafter, reflections from an upper surface 414, some of which may be absorbed as a function of acoustic impedance mismatch, may propagate through the acoustic imaging medium 412 back to the thin-film piezoelectric layer 402

In one specific implementation, the support layer 404 has a thickness of approximately 2 μm, the first electrode 518 has a thickness of approximately 0.1 μm, the thin-film piezoelectric layer 402 has a thickness of approximately 1.0 μm, the second electrode 412 has a thickness of approximately 0.1 μm, and the adhesive/epoxy layer 416 has a thickness of approximately 3 μm.

These foregoing example thickness are merely illustrative of the relative thickness of the various layers that may be appropriate in certain configurations. In many examples, different thicknesses, including relative thicknesses may be suitable, especially upon consideration of a center frequency output by and received by the controller 414.

As a result of these constructions, a stiffener layer and a backing (which may be a vacuum cavity or other sealed volume) typical of conventional pMUT/microelectromechanical transducers may be eliminated, along with manufacturing complexities and costs associated therewith. In addition, due at least in part to the reduced relative thickness of the adhesive/epoxy layer, an improved acoustic coupling between the high impedance stack of layers (such as shown in FIG. 4) and an acoustic imaging medium can be achieved. This may be particularly advantageous for coupling to certain materials such as metals or ceramics, which may be selected for electronic device housings.

As noted with respect to other embodiments described herein, each layer depicted and described with reference to FIG. 4 can be manufactured using a thin-film deposition manufacturing process. In such examples, alignment complexities and other manufacturing challenges related to tolerances can be eliminated or substantially reduced.

For example, as noted with respect to other embodiments described herein, a high impedance stack of layers forming an acoustic transducer, such as described herein can be formed along with and/or over an application-specific integrated circuit that, in turn, can be configured to perform, coordinate, trigger, or otherwise execute one or more operations of a controller or a regional gain controller such as described herein.

In addition, it may be appreciated that these foregoing example embodiments are not exhaustive of the various constructions of an acoustic imaging system, such as described herein. For example, although a single acoustic element (e.g., piezoelectric element) is depicted in FIG. 4, it may be appreciated that an acoustic imaging system such as described herein it typically implemented with multiple discrete and/or physically-separated acoustic transducers arranged in a two-dimensional array (which may be flat and/or may follow a particular curve contouring to a particular acoustic imaging medium geometry), each of which may be conductively coupled to at least a portion of an application-specific integrated circuit configured to initiate drive operations and/or sense operations leveraging said acoustic transducers. In particular, in such embodiments, the array of acoustic transducers may each include two discrete electrodes (e.g., an electrode pair) that can be individually conductively coupled to an application-specific integrated circuit, some or all of which may be physically coupled to the transducer itself, such as shown in FIG. 4.

In such embodiments, an array of electrode pairs, each of which is associated with a discrete piezoelectric actuator/acoustic transducer, can be disposed in a grid or matrix pattern, such as described above. In many cases, each electrode of an electrode pair takes the same shape and size, but this is not required; some embodiments include an upper electrode coupled to a top surface of a piezoelectric actuator that is made from a different material, in a different shape, formed to a different thickness, and so on contrasted with a lower electrode coupled to a bottom surface of the same piezoelectric actuator.

More generally and broadly, it may be appreciated that layers described above may be formed form a number of different materials, and/or may be formed in a number of suitable processes. For example, in some cases one or more electrodes of can be aluminum which may be sputtered to a thickness of 100 nm, or a greater thickness or a smaller thickness. In some cases, an adhesion layer may be formed as well to promote electrical and mechanical coupling. Titanium is one example material that may be used as an adhesion layer.

In other cases, other metals may be used for electrodes. In some examples, one electrode may be made from a first material to a first thickness (e.g., Al to 100 nm), and a second electrode can be made from a second material to a second thickness (e.g., Al/Ti to 100 nm); embodiments and implementations vary.

In some cases, a PVDF-TrFE thin-film layer can be formed by depositing a powder/solvent solution, allowing the solvent to evaporate, and thereafter annealing. In such examples, a PVDF-TrFE layer may be formed to a thickness of approximately 1.5 μm, or less than or greater than the same. Such a layer may be etched into multiple discrete regions by a suitable mechanical, chemical, electrical or other etching process such as reactive ion etching process.

These foregoing embodiments depicted in FIG. 4 and the various alternatives thereof and variations thereto are presented, generally, for purposes of explanation, and to facilitate an understanding of various configurations and constructions of a single transducer of an acoustic imaging system, such as described herein. However, it will be apparent to one skilled in the art that some of the specific details presented herein may not be required in order to practice a particular described embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions of specific embodiments are presented for the limited purposes of illustration and description. These descriptions are not targeted to be exhaustive or to limit the disclosure to the precise forms recited herein. To the contrary, it will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

For example, as noted above, in many examples an acoustic imaging system as described herein can include an array of acoustic transducers. The array of acoustic transducers can be formed such as described above, typically in a single process or set of manufacturing operations or stages. For example, the array of transducers can be defined by a number of individual acoustic transducers, each of which is defined by a portion of a thin-film piezoelectric material disposed between two electrodes dedicated to each individual acoustic transducer.

In some examples, as noted above, the array of transducers can be subdivided and/or segmented into tiles. Each tile can included dedicated electronics optimized to drive and/or sense via the acoustic transducers of that particular tile. Such constructions and configurations can dramatically improve signal to noise ratios, reduce cost, reduce power consumption, reduce contrast variability, and reduce manufacturing and signal routing complexity. FIGS. 5-7 are provided to illustrate an example construction in which a high aspect ratio (e.g., 2) array of acoustic transducers, formed in a thin-film process such as described above, are segmented.

In particular, FIG. 5 depicts a system diagram of a segmented acoustic imaging system, as described herein. In this example, an array of thin film acoustic transducers 500 can include 168 individual transducers, arrange in a rectilinear pattern of 24×7. In this example, four tiles/segments are shown, arranged in one row of four tiles. Each tile includes and is dedicated to 6×7 or 41 acoustic transducers of the 168 transducers depicted in the illustrated embodiment. In the illustrated embodiment, four tiles are identified as the first tile 502, the second tile 504, the third tile 506, and the fourth tile 508.

In particular, a first tile 502 can include 42 separate and individually addressable thin-film acoustic transducer, one of which is identified as the acoustic transducer 502 a. Each transducer of the first tile 502, including the acoustic transducer 502 a can be conductively coupled to a dedicated analog front end, the tile front end 510, via a signal bus 512.

In this construction, the tile front end 510 can be configured to receive and process and/or condition one or more analog voltage signals from one or more of the 42 acoustic transducers defining the first tile 502, including the acoustic transducer 502 a.

For example, the tile front end 510 can be configured to (in no particular order or sequence) demodulate AC signals received from the acoustic transducer 502 a, filter a voltage signal received from the acoustic transducer 502 a (e.g., frequency-domain or time-domain filters, such as band pass, low pass, high pass, moving average, and so on), amplify a voltage signal received from the acoustic transducer 502, attenuate all or some of a voltage signal received from the acoustic transducer 502 a, store acoustic energy generated by the voltage signal, integrate a time-varying voltage signal received from the acoustic transducer 502 a over a given time window which may be fixed or variable, offset and/or bias a voltage signal received from the acoustic transducer 502 a by a given amount or calibration value, and so on.

Other tiles of the array of thin film acoustic transducers 600 can be identical to the first tile 502, such as described above. For example, the second tile 504 can also include 42 independently addressable acoustic transducers. These transducers can be coupled, via a signal bus 514, to a tile front end 516 which can perform the same operations described above.

In the same manner, other tiles can be coupled each to a respective tile front end. For example, the third tile 506 can be coupled to a signal bus 518 and the tile front end 520 and the fourth tile 508 can be coupled to a signal bus 522 and the tile front end 524.

Each of the dedicated tile front ends (e.g., the tile front ends 510, 516, 520, 524) can be communicably and/or conductively coupled to a regional gain controller 526.

The regional gain controller 526 is configured to modify one or more properties and/or operational characteristics of one or more of the tile front ends in order to locally improve signal to noise ratios within particular regions of the acoustic imaging system. For example, in some implementations, the regional gain controller 526 may be configured to access a database 528 (which may be a separate database, or may be a portion of the regional gain controller 526) to obtain one or more configuration files or calibration parameters associated with particular transducers of the array of acoustic transducers. In other words, the regional gain controller 526 can be configured to customize how signals output from individual transducers of the array of transducers are processed.

For example, in some cases, a particular transducer when manufactured may have a lower dynamic range than other transducers of the array. In one examples, the transducer may output a voltage 5% lower than voltages output from other transducers of the array in the presence of the same mechanical stimulus. In this example, the regional gain controller 526 can be configured to boost the gain of one or more amplifiers in a single processing/conditioning pipeline when the defective transducer is being read. In this manner, the effective measured range of the transducer can more closely match the response of all other transistors of the array, thereby improving performance of the acoustic imaging system.

In yet other examples, the regional gain controller 526 can be configured to dynamically change one or more operational characteristics of one or more tile front ends to increase gain or decrease gain of particular regions, tiles, or areas of transducers among the array of transducers. For example, in some implementations, the regional gain controller 526 may be configured to operate the tile front end 524 in a manner that amplifies voltage signals from the fourth tile 508 more than the tile front end 520 amplifies voltage signal from the third tile 506. For example, in one embodiment, the regional gain controller 526 is configured to set a linear gain of the tile front end 524 to 1.5 and a linear gain of the tile front end 520 to 1.2. These linear gain coefficients may be stored in whole or in part in the database 528.

In other cases, the regional gain controller 526 can be configured to define one or more regions within and/or overlapping one or more tiles of the array. For example, FIG. 5 illustrates a region 530, a region 532, and a region 534 (which overlaps both the third tile 506 and the fourth tile 508). As with other embodiments described herein, the regional gain controller 526 can be configured to cause different gain characteristics to be applied to each of the illustrated regions. Additionally, the regional gain controller 526 can be configured to define any suitable number of regions, including any suitable number of transducers in each. In some examples, a region defined by the regional gain controller 526 can be a square or rectangular region. In other cases, the regional gain controller 526 can define a region of arbitrary shape.

It may be appreciated that this example construction is merely provided as one example; any suitable number or arrangement of tiles may be selected. Similarly, in some embodiments, tiles may include different numbers of acoustic transducers. In other cases, some tiles may be differently shaped than other tiles. In some cases, tiles may be enclosed within other tiles (e.g., concentric arrangements). In other cases, one tile may circumscribe another tile. In some cases, some tiles may be coupled to the at least one common transducer; in other words, some tiles may overlap such that different tile front ends may be configured to control the same acoustic transducers (e.g., for redundancy).

Similarly, it may be appreciated that each individual analog front end may be configured in the same manner, or may be configured in tile-specific ways. For simplicity of description, the embodiments that follow presume a construction in which each tile of a given embodiment has the same number of transducers and is configured to operate in identical ways. In such examples, each respective analog front end and/or the regional gain controller may be defined, at least in part, in an integrated circuit over which the acoustic transducers of that particular tile are formed, such as described above.

FIG. 6 depicts a schematic/signal flow diagram 600 of an analog front end 602 of a tile of a segmented acoustic imaging system, as described herein. In particular, the analog front end 602 receives one or more input voltage signals via the signal bus 604. The signal bus 604 can provide input to a multiplexer 606 configured to iteratively switch between individual traces of the signal bus 604 so that individual signals corresponding to outputs of individual acoustic transducers can be individually processed and/or conditioned.

The multiplexer 606 may be configured to provide as output a time multiplexed voltage signal that iteratively shifts between two or more transducers of the analog front end 602. In some examples, the multiplexer 606 is configured to linearly shift between transducers, advancing row by row or column by column. In other cases, the multiplexer 606 is configured to follow a serpentine multiplexing pattern. In yet other cases, the multiplexer 606 can be controlled at least in part by a beamforming controller informing selection among traces associated with the signal bus 606 based on a timing and/or phase difference pattern; any suitable pattern may be used, some of which may switch between all acoustic transducers, some of which may switch between only a subset of the acoustic transducers of the analog front end 602.

At a given time, an output of the multiplexer 606 may correspond to a single voltage signal generated by a single acoustic transducer. For simplicity of description the embodiments that follow reference an output of a single acoustic transducer. It may be appreciated however, that the embodiments and signal conditioning and modification operations and stages that follow may be likewise applied to any output of any suitable acoustic transducer or combination of transducers; in some examples, outputs from one or more transducers may be combined in the analog domain prior to being received by the analog front end 602.

A voltage signal output from the multiplexer 606 is provided as input to a first amplifier 608, which may be configured to amplify the voltage signal by a fixed or variable amount. A gain profile of the first amplifier 608 may be linear or non-linear. In some cases, gain may be frequency dependent. In other cases, gain may be informed by and/or based on a configuration parameter based on and/or associated with particular individual acoustic transducers. In these embodiments, manufacturing differences between individual transducers can be compensated for by varying gain of the first amplifier 608. The gain profile of the first amplifier 608 may be selected so as to not saturate downstream signal processing electronics; in some cases, maximum gain may be selected automatically as a result of feedback received from one or more downstream signal processing stages. For example, a subsequent stage may be configured to detect when that stage is saturated or otherwise operating outside of a given operational parameter. In such examples, the subsequent stage may provider operational input to the first amplifier 608 to cause the first amplifier 608 to reduce its gain, at least with respect to a particular acoustic transducer.

An amplified voltage signal is output from the first amplifier 608 and provided as input to a band pass filter 610. The band pass filter 610 may be configured to attenuate and/or eliminate both high frequency content and low frequency content from the amplified voltage signal. The band width and center frequency at which the band pass filter 610 operates may vary from embodiment to embodiment.

In many cases, as noted above, an acoustic imaging system as described herein can be configured to operate in a drive mode at a particular center frequency. For example, a pulse or input provided to a given acoustic transducer may have a center frequency at a selected and controlled value. For convenient reference, this frequency is referred to herein as the “drive frequency,” the “drive center frequency,” or more generally, the “carrier frequency.”

In these examples, the band pass filter 610 may be configured to filter the amplified voltage signal around the carrier frequency at which the acoustic imaging system operates. For example, if the acoustic imaging system is configured to operate at 10 MHz, the center frequency of the band pass filter 610 may be selected to be 10 MHz, with a bandwidth of 0.5 MHz. In other cases, other band widths and/or other center frequencies may be selected. For example, in some embodiments, a band pass filter such as the band pass filter 610 may be configured to target a harmonic of the carrier frequency. In other cases, the band pass filter 610 may have a larger band width; may configurations are possible, many of which are implementation specific.

The band pass filter 610 is configured to output a passband signal. The passband signal can be provided as input to a high-frequency rectifier 612. The rectifier 612 can be configured to be an asynchronous full-bridge rectifier or a synchronous rectifier. In many implementations, the rectifier 612 is an active, synchronous rectifier so as to reduce conduction losses and forward bias voltage drop.

The rectifier 612 may be configured to output a rippled direct current signal. In some cases, the rippled direct current signal may be applied as input to an optional low pass filter (e.g., a capacitor coupling the rippled direct current signal to ground) or other envelope following circuit.

The rectifier 612 and/or any other envelope detection circuitry can provide a rippled, frequency-limited, output voltage signal as input to an integrator 614 configured to integrate the low-frequency output voltage signal over a particular time window, which may be varied or constant.

As a result of this construction the integrator 614 can effectively provide an output voltage that corresponds, at least in part, to a quantity of acoustic energy lost during a preceding drive operation to an acoustic impedance mismatch at an imaging area/surface such as described above. More particularly, the greater an acoustic impedance mismatch between the acoustic imaging medium into which an acoustic pulse is generate (by the acoustic imaging system), the greater quantity of acoustic energy that should be received as a reflection at one or more of the acoustic transducers of the array of acoustic transducers. As one specific example, a fingerprint valley accounts for a greater acoustic impedance mismatch than a fingerprint ridge, and is thus associated with a higher amplitude of acoustic reflection. As a result, an output of the integrator 614 is expected to be greater in the presence of a fingerprint valley than a fingerprint ridge.

As may be appreciated by a person of skill in the art, different acoustic impedance mismatches may result in different quantities of acoustic energy being received as a reflection at the acoustic imaging system. In particular, it may be the case—especially for particular acoustic media such as metals—that the overwhelming majority of acoustic energy received is from the drive signal itself. In another non-limiting phrasing, carrier noise dominates the signal received at the integrator 614.

To account for carrier noise, many embodiments include an offset digital to analog converter 616 configured to provide a fixed or variable voltage output as input to the integrator 614 so that carrier amplitude and/or carrier noise can be subtracted in real time from the output of the integrator 614. The offset digital to analog converter 616 can be configured to receive a digital control signal that defines a bias level output by the offset digital to analog converter 616. The control signal can provide a fixed voltage or a variable digital voltage based at least in part on a drive signal applied to one or more acoustic transducers. The digital control signal can provide a digital bias value that is based, at least in part, on feedback from an upstream or downstream signal conditioning stage. It may be appreciated by a person of skill in the art that the offset digital to analog converter 616 can provide any suitable offset that may vary based on beamforming operations, a position or physical location of a particular acoustic transducer, a waveform selected to drive at least one acoustic transducer, a type or characteristic of an acoustic imaging medium and so on.

As a result of this construction, the integrator 614 can be configured to provide a conditioned signal, without carrier interference, via an output 618. As noted above, each tile of a given array can be configured to operate in the same manner as the first tile 608.

In addition, the analog front end 602 can be communicably coupled to a regional gain controller 620. As with other embodiments described herein, the regional gain controller 620 can be communicably and/or conductively coupled to one or more operational components of the analog front end 602 to customize the behavior of the analog front end 602 based on a particular signal's physical source (e.g., which transducer and/or which region and/or which tile that signal originated from).

For example, the regional gain controller 620 can be communicably coupled to the first amplifier 608. In some examples, the regional gain controller 620 can be configured to access a database 622 to obtain a gain factor for the first amplifier 608 given a particular signal's origin (i.e., which transducer originated the signal and/or what region that transducer is associated with). In some cases, the regional gain controller 620 can cause the first amplifier 608 to amplify the voltage signal output from the multiplexer 606 by a default, standard, or normal amount. In other cases, the regional gain controller 620 can cause the first amplifier 608 to attenuate the voltage signal output from the multiplexer 606. In yet other examples, the regional gain controller 620 can cause the first amplifier 608 to attenuate the voltage signal output form the multiplexer 606. In some embodiments, to increase contrast in a resulting resolved image, the regional gain controller 620 can be configured to boost output of the first amplifier 608. In other cases, to increase contrast, the regional gain controller 620 may be configured to reduce or attenuate output of the first amplifier 608. As may be understood by a person of skill in the art, amplifier characteristics may be modified in a number of suitable ways.

In other cases, the regional gain controller 620 can be coupled to the band pass filter 610 and/or the rectifier 612, each of which may have selectable gain factors in some implementations.

In yet other examples, the regional gain controller 620 can additionally or alternatively communicably and/or conductively coupled to the offset digital to analog controller 616. As with other embodiments described herein, in some examples, the regional gain controller 620 can be configured to access the database 622 to obtain a gain factor for the offset digital to analog controller 616 given a particular signal's origin. In some cases, the regional gain controller 620 can cause the offset digital to analog controller 616 to amplify the digital signal output from the integrator 614 by a default, standard, or normal amount. In other cases, the regional gain controller 620 can cause the offset digital to analog controller 616 to reduce the digital signal output from the integrator 614. In yet other examples, the regional gain controller 620 can cause the offset digital to analog controller 616 to reduce the digital signal output form the multiplexer 606. In some embodiments, to increase contrast in a resulting resolved image, the regional gain controller 620 can be configured to increase digital output of the offset digital to analog controller 616. In other cases, to increase contrast, the regional gain controller 620 may be configured to reduce output of the offset digital to analog controller 616 by a linear or non-linear amount. As may be understood by a person of skill in the art, amplifier characteristics may be modified in a number of suitable ways.

These foregoing embodiments depicted in FIGS. 4-5 and the various alternatives thereof and variations thereto are presented, generally, for purposes of explanation, and to facilitate an understanding of various configurations and constructions of a segmented/tiled acoustic imaging system with a hierarchy or staged arrangement of signal conditioning, such as described herein. However, it will be apparent to one skilled in the art that some of the specific details presented herein may not be required in order to practice a particular described embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions of specific embodiments are presented for the limited purposes of illustration and description. These descriptions are not targeted to be exhaustive or to limit the disclosure to the precise forms recited herein. To the contrary, it will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

For example, as noted above, an output of an individual tile can be provided as input to a single shared signal conditioning/analog to digital converter stage, which may also be configured to couple to and/or be configured at least in part by a regional gain controller such as described herein. FIG. 7 depicts a system diagram of a segmented acoustic imaging system, as described herein.

As with other embodiments described herein, the acoustic imaging system 700 includes a drive controller 702 that provides drive signals (which may have particular phase and/or waveform characteristics, following a beamforming pattern or scan plan) to one or more tiles and/or one or more individual acoustic transducers of an array of thin-film acoustic transducers 704. As noted above, the array of thin-film acoustic transducers 704 may be segmented into tiles, each of which may be associated with a dedicated one analog front end; collectively tile-level analog front ends are illustrated as the front ends 706.

Output from the front ends 706 can be provided as input to single shared analog to digital converter stage which can be tasked with, and configured to, provide a digital output value that corresponds to acoustic impedance mismatch at a particular location of an imaging surface or imaging area associated with the acoustic imaging system 700.

More particularly, as noted above with respect to FIGS. 2A-2C, the drive controller 702 can include an oscillator configured to provide a stable high frequency signal that may be sampled to generate one or more drive signals that, in turn, can be applied as input to one or more acoustic transducers of the array of thin-film acoustic transducers 704.

In many examples, the oscillator is configured to oscillate at a stable frequency in the tens of MHz (e.g., 10 MHz, 20 MHz, 50 MHz, and so on), but this is not a requirement and a person of skill in the art may readily appreciate that different—either higher or lower—frequencies may be appropriate in particular embodiments.

The oscillator can be kept in phase relative to other signal lines of the system by a phase lock loop. In many examples, the phase lock loop is configured to synchronize the oscillator—or an output thereof—with a system clock and/or a harmonic thereof. As a result of this construction, downstream electronics, especially digital electronics, can be synchronized in with high frequency signals used in the analog domain to generate drive signals such as described above.

An output of the phase lock loop can be provided as input to a phase generator which can be configured to provide outputs via a signal bus, each of which represent a differently-delayed/differently-phased signal output from the phase lock loop. For example, in some embodiments the phase generator may be configured to provide eight signals as output; a first signal line transits a voltage signal precisely in phase with output of the phase lock loop, a second signal line transits a voltage signal 22.5 degrees out of phase with the output of the phase lock loop, a third signal line transits a voltage signal 45 degrees out of phase with the output of the phase lock loop, and so on.

Signals carried by the signal bus can be provided as input to a multiplexer that can be driven by a drive selector. The drive selector can be configured to select which signal line (i.e., which phase delay) to apply at a particular moment. As may be appreciated by a person of skill in the art, the drive selector can leverage one, and/or be leveraged by, or more beamforming controllers that operate by applying differently-phased signals to differently located acoustic transducers.

An output of the multiplexer, selected by the drive selector, can be provided as input to an address selector configured to provide the output to a particular selected acoustic transducer of the array of thin-film acoustic transducers 704 via an output signal line. The address selector can be configured to cooperate with the drive selector or may operate independently; many configurations and control paradigms are possible.

The signal carried by the output signal line can be received at the intended, addressed, acoustic transducer of the array of thin-film acoustic transducers 704, which may be a member of any other suitable tile and/or may be defined as a member of any particular region.

As a result of this construction, when the target acoustic transducer receives the signal carried by the output signal line, the target acoustic transducer generates a mechanical output into an acoustic imaging medium that has a center frequency based at least in part on the operating frequency (or a harmonic or sampled multiple thereof) of the oscillator of the drive controller 702.

As described with respect to other embodiments described herein, substantially immediately after a drive operation has been triggered, a sense operation may be initiated in which one or more voltage signals generated by one or more acoustic transducers of the array of thin-film acoustic transducers 704 (which may include the target acoustic transducer) can be received via a signal bus at a tile-specific front end. The tile front end can operate in much the same manner as described above in reference to FIG. 6; this description is not repeated.

The tile front end—and/or other tile front ends—can provide output thereof to a multiplexer 708 of the single shared analog to digital converter stage. The single shared analog to digital converter stage 708 can provide output to another amplifier, identified as the post-integration amplifier 710. As with other amplifiers described herein, the post-integration amplifier 710 can be configured to operate according to any suitable variable or fixed gain profile.

The single shared analog to digital converter stage 708 also includes a high frequency and high fidelity analog to digital converter 712. In some embodiments, a successive approximation analog to digital converter can be used; although this is not required of all embodiments.

The high frequency and high fidelity analog to digital converter 712 can provide a digital output to subsequent digital-domain processing systems, such as a digital image processor 714 and/or an image correction or recognition processor 716.

As with other embodiments described herein, any digital domain or analog domain signal-modifying component can be communicably coupled to and/or may be partially controlled by a regional gain controller 718.

For example, any one of the tiles 704 can be controlled, at least in part, by the regional gain controller 718. More specifically, the regional gain controller 718 can access a database 702 to obtain one or more values or coefficients that are associated with a particular transducer, region of transducers, or tile of transducers. This value can be used to inform operation of a preamp circuit associated with an individual transducer or set of transducers (however organized; as a region or as a tile.

In addition or in the alternative, any one of the analog front ends 706 can be controlled, at least in part, by the regional gain controller 718. More specifically the regional gain controller 718 can access the database 720 to obtain one or more values or coefficients that are associated with a particular transducer, a particular region of transducers, or a particular tile of transducers of an array. For example, as described above in reference to FIG. 6, the regional gain controller 718 can be configured to modify a gain factor of a first amplifier, a band pass filter, a carrier-correction offset DAC, and so on.

In addition or in the alternative, an operation of and/or a gain factor of the post-integration amplifier 710 can be controlled by, at least in part, by the regional gain controller 718. More specifically the regional gain controller 718 can access the database 720 to obtain one or more values or coefficients or profiles that are associated with a particular transducer, a particular region of transducers, or a particular tile of transducers of an array.

In further examples, the regional gain controller 718 can be coupled to the shared digital to analog converter 712 to inform an output bias thereof.

In yet other examples, the regional gain controller 718 can be configured to receive input from the digital image processor 714 and/or the image correction or recognition processor 716. More specifically, either or both of these elements may be configured to detect areas or regions of insufficient or suboptimal contrast. In response, either element can instruct the regional gain controller 718 to update or otherwise change a gain of one or more amplifiers or signal conditioners in order to improve contrast.

More broadly, it may be appreciated that a regional gain controller as described herein can be configured to modify any operational parameter of any stage in an analog to digital signal conversion and conditioning chain in order to improve contrast thereof.

These foregoing embodiments depicted in FIG. 7 and the various alternatives thereof and variations thereto are presented, generally, for purposes of explanation, and to facilitate an understanding of various configurations and constructions of an acoustic imaging system, such as described herein. However, it will be apparent to one skilled in the art that some of the specific details presented herein may not be required in order to practice a particular described embodiment, or an equivalent thereof.

Thus, it is understood that the foregoing and following descriptions of specific embodiments are presented for the limited purposes of illustration and description. These descriptions are not targeted to be exhaustive or to limit the disclosure to the precise forms recited herein. To the contrary, it will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

For example, although signal lines in FIGS. 5-7 are illustrated as single signal lines, in many embodiments, multiple lines may be leveraged to convey differential signals.

In other examples, the acoustic imaging system 700 can be further configured for dark pixel subtraction. In such cases, a test controller may be configured to provide a test signal to drive one or more acoustic transducers at a particular selected moment at which no imaging input is expected. Thereafter, output from the analog to digital converter 712 and/or another signal processing or signal conditioning stage can be used and/or stored to be subtracted at a later time during an imaging or sensing operation.

In yet other examples, additional carrier rejection operations can be performed in addition to the carrier subtraction/offset digital to analog converter described above in reference to FIGS. 5-6. For example, in some embodiments I-Q demodulation may be leveraged to mitigate effects of carrier noise. In other cases, envelope detection and/or following may be employed. In yet further examples, device specific and/or pixel specific configuration or calibration parameters can inform operations of the acoustic imaging system 700; some acoustic transducers and/or tiles may be associated with higher or lower gain than other acoustic transducers or tiles. Such example embodiments can be described as region-specific gain control embodiments.

In yet other examples, beamforming may be used for mechanical/analog carrier noise rejection.

The foregoing example embodiments are not exhaustive of the various methods of operating a system as described herein. As such, generally and broadly, embodiments described herein reference an array of acoustic transducers, formed using a thin-film deposition and/or manufacturing process, that are formed atop an application-specific integrated circuit which may form a part of a transducer specific circuit (e.g., preamp, charge binning, and so on), a tile-specific circuit, or a shared circuit.

Generally and broadly, FIGS. 8-9 are flow charts that depict example operations of methods of operating an acoustic imaging system as described herein.

FIG. 8 is a flowchart depicting example operations of a method of operating a thin-film acoustic imaging system including a regional gain controller, such as described herein. The method 800 includes operation 802 at which a transducer and/or tile to operate in a sense mode is selected. Next, at operation 804, a gain profile associated with the selected transducer or group of transducers is selected, optionally from a database. The gain profile can include individual gain coefficients for multiple signal processing stages, in either the analog or digital domain, whether before or after integration, and so on. The method 800 also includes operation 806 at which the selected profile is applied to at least one digital or analog element.

FIG. 9 is a flowchart depicting example operations of another method of operating a thin-film acoustic imaging system including a regional gain controller, such as described herein. The method 900 includes operation 902 at which feedback is received regarding quality of an output image. Next at operation 904, a region in which to improve contrast and/or change or adjust a gain profile is identified. Finally, at operation 906, at least one gain parameter of the selected region is modified.

One may appreciate that although many embodiments are disclosed above, that the operations and steps presented with respect to methods and techniques described herein are meant as exemplary and accordingly are not exhaustive. One may further appreciate that alternate step order or fewer or additional operations may be required or desired for particular embodiments.

Although the disclosure above is described in terms of various exemplary embodiments and implementations, it should be understood that the various features, aspects and functionality described in one or more of the individual embodiments are not limited in their applicability to the particular embodiment with which they are described, but instead can be applied, alone or in various combinations, to one or more of embodiments, whether or not such embodiments are described and whether or not such features are presented as being a part of a described embodiment. Thus, the breadth and scope of the claimed subject matter should not be limited by any of the above-described exemplary embodiments but is instead defined by the claims herein presented.

The present disclosure recognizes that personal information data, including biometric data, in the present technology, can be used to the benefit of users. For example, the use of biometric authentication data can be used for convenient access to device features without the use of passwords. In other examples, user biometric data is collected for providing users with feedback about their health or fitness levels. Further, other uses for personal information data, including biometric data, that benefit the user are also contemplated by the present disclosure.

The present disclosure further contemplates that the entities responsible for the collection, analysis, disclosure, transfer, storage, or other use of such personal information data will comply with well-established privacy policies and/or privacy practices. In particular, such entities should implement and consistently use privacy policies and practices that are generally recognized as meeting or exceeding industry or governmental requirements for maintaining personal information data private and secure, including the use of data encryption and security methods that meets or exceeds industry or government standards. For example, personal information from users should be collected for legitimate and reasonable uses of the entity and not shared or sold outside of those legitimate uses. Further, such collection should occur only after receiving the informed consent of the users. Additionally, such entities would take any needed steps for safeguarding and securing access to such personal information data and ensuring that others with access to the personal information data adhere to their privacy policies and procedures. Further, such entities can subject themselves to evaluation by third parties to certify their adherence to widely accepted privacy policies and practices.

Despite the foregoing, the present disclosure also contemplates embodiments in which users selectively block the use of, or access to, personal information data, including biometric data. That is, the present disclosure contemplates that hardware and/or software elements can be provided to prevent or block access to such personal information data. For example, in the case of biometric authentication methods, the present technology can be configured to allow users to optionally bypass biometric authentication steps by providing secure information such as passwords, personal identification numbers (PINS), touch gestures, or other authentication methods, alone or in combination, known to those of skill in the art. In another example, users can select to remove, disable, or restrict access to certain health-related applications collecting users' personal health or fitness data. 

What is claimed is:
 1. An acoustic imaging system comprising: an array of acoustic transducers; an integrated circuit formed below the array of acoustic transducers and comprising: a first amplifier stage configured to receive a voltage signal from at least one acoustic transducer of the array of acoustic transducers; a band pass filter stage to receive a first amplified output of the first amplifier stage; a rectifier stage to receive a filtered output of the band pass filter stage; an integrator stage to receive a rectified output of the rectifier stage; and a second amplifier stage configured to receive an integrated offset output of the integrator stage; and an analog to digital converter configured to receive a second amplified output of the second amplifier stage, the analog to digital converter stage configured to output a digital value corresponding to the voltage signal; and a regional gain controller configured to adjust a gain profile of at least one of the first amplifier or the second amplifier based at least in part on a location within the array of acoustic transducers of the at least one acoustic transducer.
 2. The acoustic imaging system of claim 1, wherein the regional gain controller is conductively coupled to at least one of the first amplifier or the second amplifier.
 3. The acoustic imaging system of claim 1, wherein the regional gain controller is configured to adjust the gain profile of at least one of the first amplifier or the second amplifier in response to a determination that the at least one acoustic transducer is within a defined region of the array of acoustic transducers.
 4. The acoustic imaging system of claim 1, wherein the regional gain controller is configured to retrieve the gain profile from a database in communication with the regional gain controller.
 5. The acoustic imaging system of claim 4, wherein the regional gain controller comprises the database.
 6. The acoustic imaging system of claim 1, wherein the array of acoustic transducers is defined by: a thin-film piezoelectric layer; a first electrode layer defining a first array of electrodes formed below the thin-film piezoelectric layer; and a second electrode layer defining a second array of electrodes formed below the thin-film piezoelectric layer.
 7. The acoustic imaging system of claim 1, wherein the thin-film piezoelectric layer is formed from PVDF.
 8. The acoustic imaging system of claim 1, wherein the thin-film piezoelectric layer is formed, at least in part, from TrFE.
 9. The acoustic imaging system of claim 1, wherein the thin-film piezoelectric layer is a monolithic layer.
 10. An acoustic imaging system comprising: an array of acoustic transducers arranged as a set of tiles, each respective tile comprising an analog front end comprising a first amplifier stage configured to amplify a first voltage signal output by at least one acoustic transducer of the respective tile; an integrated circuit coupled to each analog front end of each tile and comprising a second amplifier stage configured to amplify a second voltage signal output by at least one analog front end; and an analog to digital converter coupled to the integrated circuit and configured to sample and convert a third voltage signal output by the integrated circuit to a digital domain signal; and a regional gain controller configured to adjust a gain profile of at least one of the first amplifier, the second amplifier, or the analog to digital converter based at least in part on a location within the array of acoustic transducers of an acoustic transducer that generated the first voltage signal.
 11. The acoustic imaging system of claim 10, wherein the regional gain controller is a portion of the integrated circuit.
 12. The acoustic imaging system of claim 10, wherein the regional gain controller is configured to adjust a first gain profile of the first amplifier and a second gain profile of the second amplifier.
 13. The acoustic imaging system of claim 10, wherein the regional gain controller is configured to adjust the gain profile in response to feedback received form the integrated circuit.
 14. The acoustic imaging system of claim 10, wherein at least one acoustic transducer of the array of acoustic transducers comprises a thin-film piezoelectric material.
 15. The acoustic imaging system of claim 14, wherein the thin-film piezoelectric material comprises PVDF.
 16. A method of signal processing in an acoustic imaging system, the method comprising: receiving a voltage signal from an acoustic transducer of an array of acoustic transducers of the acoustic imaging system; amplifying the voltage signal with a first amplifier configured according to a first gain profile selected in part based on a location of the acoustic transducer to output an amplified voltage signal; filtering the amplified voltage signal through a bandpass filter to output a filtered signal; rectifying the filtered signal to output a rippled voltage signal; integrating the rippled voltage signal to output an integrated signal; amplifying the integrated signal with a second amplifier configured according to a second gain profile selected in part based on the location of the acoustic transducer to output an analog signal; and converting the analog signal into a digital signal with an analog to digital converter.
 17. The method of claim 16, wherein converting the analog signal into the digital signal is performed by an analog to digital converter configured according to a third gain profile selected in part based on the location of the acoustic transducer.
 18. The method of claim 16, wherein the acoustic transducer is within a defined region of the array of acoustic transducers.
 19. The method of claim 18, wherein the first gain profile is selected in part based on the defined region.
 20. The method of claim 18, wherein the first gain profile and the second gain profile are selected in part based on the defined region. 